Subjectivity defined as "what consciousness feels like to itself", for purposes here.
First, explain "feels like": Feeling begins in the body and is an immediate-immanent awareness of a difference at the physiological level, that difference being represented in neurological correlates as a change in neural patterns; the internal 'model' of the body extends across time and as such is capable of registering changes in so far as the present moment body-model can differ from the body-model that was the case in the recent past. Since memory retains the former body-models to a certain degree there is comparison of body-models from one moment to the next, and this comparison produces a meta-model that includes the different body-models as their differences, so that the meta-model is static in a way that the individual body-models are not.
The meta-model is like a derivative of a function in calculus: it is a single 'static' image yet contains in that frozen structure a recognition of changes. In calculus the d(f(x)) [f'(x)] shows in a snapshot just how f(x) is changing over time, implicitly as a rate-- this means also as a ratio which as you know I have explained as entirely objective (without units). The meta-model of the body's self-image is just like this, and is objective with respect to the 'units' of that same body-model canceling each other out on both sides of the derivative. The meta gives an immediate knowledge of the ratio of change taking place in the body at the physiological level.
Therefore this D(x) can be used as a template for what is a feeling: a feeling is a calculus-like derivative wherein rates of change are encoded as frozen knowledge. Values are now imposed upon the meta-model in order to orient feelings with respect to meaning; in animals this meaning is largely genetically given, and supplemented by remembered experiences of the organism itself, while in humans this meaning is that animal formula plus the addition of existentiality, or what I call "factness", which is to say that a vastly extended sphere of significance, consequence, prediction and expectation, and memory all supplement the meaning by forming meaning into capable of participating with/in ideation.
Thus a feeling is the frozen structure of encoded changes qua implicit meaning-giving at the behest of a pre-existing meaningful structure of standards of measure. Physiological-instinctive for animals, and physiological-instinctive + existential for humans.
Now, subjectivity as "the feels like to itself of consciousness" is easily derived as follows:
I. Every conscious moment contains awareness of objects that we perceive; each object we perceive has a past construct associated with it that allows us to grasp what that object is; each object therefore has two dimensions, its uniqueness and its general form; both an object's uniqueness and its general form are capable of provoking recollections of previous experiences we have had; every recollection of a previous experience also has two dimensions, the unique experience as such and the general forms of that experience, and both of those dimensions contain implicitly encoded within them and as the memory also memories of the feelings that were the case at the time of the original experience; when we recall an experience in memory some of the feelings that were part of the original experience are also recalled, so that we feel a little bit of the same feelings that were originally the case of the original experience now remembered.
II. Every present moment of conscious experience includes awareness of numerous objects; each object we are aware of triggers a remembrance-stream whereby something is recalled from memory of a past experience of ours that took place wherein said object either as unique or general form was at that previous time also the case for us; a small bit of feeling from the past therefore invades the present every time a presently perceived object triggers a remembrance-process; most of these feelings are much more vague and lesser in quantity of feeling than either the original feeling of that past moment or the feelings we are presently feeling as part of our present moment of consciousness; due to the proliferation of multiple layers of past experiences for every one present experience it is the case that there are many more recalled feelings from the past than there are present feelings, although the recalled ones are as previously stated much weaker and more vague than are present feelings; therefore the much larger number of recalled feelings compared to present feelings, in combination with how much stronger present feelings are compared to recalled feelings, means that recalled feelings form a background on which present feelings exist as foreground.
III. A new meta-feeling is produced as the foreground present feelings are immanently contrasted with the background recalled past feelings; this produces a new D(x); there are now two D(x) that are the case, this new one and the one originally stated as part of the body-model of physiological changes; any given moment of consciousness contains both derivatives as part of its structure of consciousness, namely we are always intuitively aware of how we feel as a whole body over time changing and of how the objects we experience are connected into our present and past meanings. Body-feeling meaning as D(x) 1 and object-feeling meaning as D(x) 2 combine to produce a very large field of multi-dimensional feelings that are always the case in some configuration at any given moment of present consciousness; because both D1 and D2 are made out of feelings they are able to co-exist within the same structural space and time moment, although the fact that the nature of the feelings in D1 and D2 are different from one another (they come from different sources and have/represent different meanings) means that while these feelings do mingle together as part of the same larger structure it is also the case that D1 and D2 meanings tend to be somewhat categorically different from one another.
Finally, what we call subjectivity is the fact that "what consciousness feels like to itself" is a combination of this D1 and D2. Partial but imperfect combination is the case, because of how both types of feeling both coincide together as part of the same structure and yet are also somewhat categorically different from one another. Thus there is a "geometry" at all times the case and which arises as a consequence of this possible yet imperfect combination of D1 and D2, this geometry being a meta-meta derivative containing as much as possible the sum total of all contents of consciousness able to be structurally present and/or significant to consciousness at any given present moment of consciousness. This "geometry" is what is called subjectivity.