Note that the Constitution seems the right size to fit into either of the 'hangers' on those stations. Well, their height certain suggests this. What's the inner width of the hanger, and is that greater than the width of the Connie?
Imagine if the Regula station was intended to be *much* larger than the Enterprise...
Of course this DOES have problems like "Why such a large station for..." and "... hoow?" But it saves us the problems of say... having multiple stations of visually identical but different physical dimensions... and also say that Regula One was a Fleet Supply Base. (... Speaking of size, K-7 seems awefully ... small to be a 'deep space station'). It was disused and slated for the SCE to dismantle it so the physical resources could be used to construct new stations nearer to the then-borders of Federation space, but the Project Genesis team convinced Starfleet to "lend" the station to them for the project. Security wise, 'No there's no one there, it's a disused station that has been almost entirely mothballed, and we just dont have the ships to dismantle it at this time' is a good cover, instead of having to explain why a station suddenly popped up out of nowhere to people in starfleet/etc who don't know about P.G. Because it DOES look like what a supply base would look like - it even has those huge tanks!
And then the 'Arms' that connect the many modules of the original Orbital Office model gain a sense of purpose - they're like a spider web of docking ports for starships, swappable with modules to expand the habitat of the stations. The section with the two hanger doors is like a mini-spacedock-esque drydocking facility, one way in, one way out.. allowing the station to perform repair and refit operations.
And then the Ptolemy's ability to daisy-chain tanks gain purpose - because really, there wasn't a single station that had the storage capacity of even one - the Regula would only need One of the tank containers of the Ptolemy...
In the current Regula-One size, those little round modules are what, one-deck tall and basically only usable as office spaces With A View? The hanger structures are basically in the shuttlecraft hanger size range. Also, the smallest sizes of module on the office complex... those are... like... really small... a few rooms max.