Funny, I happen to have this image sitting on my desktop right this minute (unless you're thinking of an image OTHER than the debris field scene, in which case I don't have a clue what you're talking about). The Lexington's saucer appears to be the same size as the Enterprise's saucer, the only difference being the former is turned perpendicular to the latter, and Enterprise is rolled almost 45 degrees to port.That makes no sense... The Lexington is another Connie. Why would it be any larger?
There's a VFX shot of the Lexington BEHIND the Enterprise where the Lexington saucer is LARGER than the whole of the Enterprise. Oddly, this shot was chosen as a promo screenie.
Intents change as the desired result changes. Remember, Gene originally intended Enterprise to turn transparent whenever it was at warp; likewise, the Klingon bird of prey was originally intended to be a Romulan vessel.Design intent, in my case, which has her being just a little over the TMP version of the ship.
Intent only goes so far, at some point you still have to reconcile it with the FINAL design through some kind of in-universe logic.