To be fair, the way the models are shot distorts them much more than any details of their construction. And on the original VCR-standard material it's not that easy to argue "this is the 4-footer! That is the 6-footer!" if one doesn't a priori know that there exist two different models; it's all attributable to differences in lighting and shadowing and camera positioning unless we choose to insist it isn't. Just look at the two screencaps on Drex Files: choosing identical angles and lenses would remove the seeming difference in dimensions or detailing (even though it so happens that certain angles and lenses would be incompatible with the smaller model).
Really, painstaking researching of model dimensions is often an inferior tool for describing the supposed spacecraft, because models are fakes: they take shortcuts, they introduce smoke and mirrors, false perspectives, painted detail that mimics raised detail and vice versa, etc, etc. A perfect replica of the main TOS photographic model would make for a piss-poor "Constitution class starship", for example, considering how shoddily the model was built and treated and how asymmetric it ended up being when shot.
It shouldn't be difficult to believe in an unchanging E-D that is somewhere between the existing models, since nothing obvious was changed from model to model. The E-E, OTOH, had distinct changes built in, and there we have to believe in some sort of a refit (even though we may choose to disregard the slight change in secondary hull shape, which would be a massive in-universe change, and merely accept the new weapons, new pylons, new neck structures and other in-universe trivialities).
Timo Saloniemi