Can't really say that I see that. If the Romulans truly wanted a more efficient design, then I think they would have opted for a tighter, more compact configuration that would have required less materials to build with.
What could they make tighter or more compact, while retaining these external dimensions (which is the very point)?
Starfleet generally agrees with the Romulans that it's not a good idea to put things between nacelles. But Starfleet wastes the space above the nacelles of an Enterprise
-shaped vessel, while the Romulans do not. Apart from that, the D'Deridex
and the Enterprise
are pretty much the same vessel, even if the primary hull of the Romulan ship is a lump and the primary hull of the Starfleet ship is a saucer (again a design with a poorer volume-to-maximum-dimensions ratio).
Pushing the nacelles closer together might be an option for reducing one maximum dimension - but Starfleet doesn't go for it. And since Starfleet keeps the nacelles widely separated, Starfleet ships are free to have primary hulls that reach out in the same maximum dimension direction. By that logic, the Romulans could have a beamier primary hull, too. But they put hull volume into the upper and lower "pylons" or "wings", thus at least reaching parity with the Starfleet configuration and probably doing better.