I noticed however reading back over mine own magnificent words, it's not entirely clear why that stuff isn't Si. Discovering forms in the stream and screwing around with them in your head is Si too. Different content, obviously. ("Obviously"?) But same process.
It's interesting though. I think perception cannot possibly exist if it lacks either of S or N. Which is to say, there is literally no way to appreciate a sense datum if there is no way to connect sense data. For consider: if you can't connect a sense datum with anything, then you can't make associations with prior sense data, nor can you determine even whether the incoming datum has any form at all, so what's there to 'appreciate"? Ergo, you positively require (a) senses and (b) some cognitive tool for associating sensations. What's really interesting, perhaps, is that condition (a), the senses, are neither S nor N, and (b), the cognitive tool, is neither the S nor the N alone, but the two of them together functioning as a unit.
So interesting then that some people have the unit as Ne/Si and others have it as Ni/Se.
yeah. to me it's always been easier to reconcile if you think of both as two parts of one whole (when in reality, there aren't two parts, there's not even a division; it's more like an oddly shaped thing where one area get's more conscious attention). and even then, to notice that the inferior isn't going to be the "smaller" piece, but the larger one since your consciousness itself would be like a child compared to the rest of your mind (in which case, none of us are really a type, or if we are, the type we claim to be is really the opposite of our true selves, but all of that would hinge on what you called the "true self").
in any case, i think you're right in saying that neither are S or N, at least to begin with. it's just "something" that may become S+N, and not in a ratio form such as 85% N and 15% S, but in the way that each is changed depending on the makeup of the individual. so, if you have S in the inferior, it's still S but it won't be or function the same way S would for an S-dom., that is, having S unconsciously will be different that having it consciously.
to me, it would make since if it was just some nebulous thing (no need to label or define it yet), and depending on how one's psyche was structured, that "thing" would begin to have human perception projected onto it, separating certain pieces from each other in a fashion that our minds can understand that we then call N and S (a human convention), and then from there it would be in it's purest form in whatever area had the most concentrated conscious energy (but even then, "purest" may be a bias because we think that our conscious selves are our real selves, in reality it's just the sides we're most acquainted with), with it's opposite falling into a realm that is relatively "un-human", in the process of doing so it (i think) would be fundamentally changed.
so, maybe for an S-inferior, they wouldn't pay as much attention to sensory detail or to a stored vision of reality (in the here-and-now sense that is taken and morphed into a more intimate image--Si), but it would still, i think, act as an unconscious base on which the intuitions can now spring from or connect.
and when you think about it, if you could envision each P-function as having two sides, it seems as if one side would always connect to another in some sort of similarity, while simultaneously having the other side oppose that connection and fall into a similarity with side of another function.