"Are we talking cross purpose about the same thing? If the forced perspective set were built as it appears, the tubes would run back about 100' or so. If I could, I would like to show that on the deck plans (but alas...)"
First, I'd like to mention that you could be correct about the "missing" beginning of the turbo lift ride in U.C. We hear the log entry of Kirk and the actual dialogue does not start until they are in the turbo lift (though the turbo lift acceleration sound may
be an issue unless they just changed from horizontal to vertical travel the moment McCoy delivers his opinion).
I do have doubts whether the corrected forced perspective would yield a length of 100' / 30 meters. I think Kirk's movement in front of the cathedral in "The Changeling" gives us an idea of the real size of the first tube frame. Assuming these pipes do not gain (!) in diameter the further the cathedral extends, the space in between these is 1.5 - 2 times that of each forward or (smaller) aft tube. If you take the far end of the cathedral as a reference point (and ignore the tube diameter) you'll get a bigger depth but an odd looking much wider space between these tubes, IMHO.