Hope come only the saucer section is visible in the first shot, did the nacelles and secondary hull fall off?
As she skidded along, the secondary hull was sheered off hitting the shore line, the saucer kept on going, the nose was caught and up ended the whole thing.
And the "gap" is much bigger, the part of the building that Khan lands on is only really half way down the cutut, he skids some distance before the shadow of the hull resumes across the building.
Why do you ignore the "evidence" from the movie: one of the only times we actually get a quoted length for scale. He jumps from the bridge, across the gap (approx 30m), and slides down the saucer. It doesn't matter how much of the saucer is exposed or whatnot.
Oh, and one more point: Scotty sizes up the airlock door on the Vengeance. "About 4 square metres", which puts them at 2.5m across (as I estimated for the ones on the Enterprise).