Frank Kogan

The all-in-one-go at-every-stage front-back-and-insides object is a noumenon, by Kant's definition. It is beyond us to perceive in this manner, yet -- in his argument -- this is how the world "out there" actually exists. For whatever reasons (Darwinian, perhaps: but of course Darwin came many decades later) our actual physical bodies and their workings decline to grasp the "whole" (the noumenon) in one go. We vastly prioritise the facing side of things nearby, right now. We -- as conscious entities -- pass across or through the noumenon in a particular, limited, filtered, finite way.
Berkeley -- for example -- argued that "outside" didn't exist at all (this Kant refers to as dogmatic idealism). Descartes proposed non-existence in order to focus on what he considered an infallible judgment (this Kant refers to as problematic idealism). Kant's argument is that the noumenon has to exist, and "outside" any given consciousness, because there has to be something that anchors and keeps distinct the "movie-images" to come together to give us the sense of time passing, which is a necessary ground for consciousness-as-we-experience-it. But ff cap-T Time inhered in the noumenon -- rather than arriving as a consequence of the machineries of our perceptual porocesses -- outside and inside would collapse together; Berkeley's idealism might as well be true, and consciousness as we know it -- including ourself the existing self -- would not be possible (oof: something like that, anyway...)
Kant and Kantian historiographers incorrectly project back onto earlier philosophy
This is true if a little unfair: in a book of 700 pages, Kant devotes three and a bit to a sketchy restatement of the entire history of philosophy, insofaras it pertains to his object of interest. So yes, he does somewhat recruit his predecessors to one or other side of the argument he is resolving. But he isn't claiming that everything they said boils down to this -- even if his professionalising successors decided that's what he meant. My assumption is that he hoped, with the Critique of Pure Reason, to DISPENSE once and for all with a particular annoying distraction of a conundrum, raised implicitly by Descartes and explicitly and provocatively by Hume. So that we could go back to eg Plato and Epicurus and Aristotle and etc, and strip out this small annoying section -- as a problem solved by Kant by Copernican means -- and concentrate on everything ELSE they discussed.

(ok i still haven't got to any of the actual puzzling questions you asked about, re sentences and etc)