You provided a relevant informational update, DavidLancaster. Thank you.

I ran some tests using 3DGS version 6.40.5 and it seems I couldn't truly reproduce my issue in an extremely simple, reduced, test level under various conditions.
c_moving player on floor (inside) of large tunnel-like poly-structure (.mdl; polygon = on):
*size increase of poly-structure: no
*slight offset of poly-structure from center axis in MED: no
*increase of polygon count of poly-structure (approx. 1800): no
*poly_collision = 2: no
*increase of polygon count of player: no
*for player, serious 'animation frame' movement of mesh relative to first frame and axis in MED: no
*intentional intersection of small poly-structure and larger poly-structure: no

I think my worthless 'bounding box intersection correction theory' is, for the most part, kaput.