Suits me fine - it means that Scotty crawled at least a little way into the bowels of the antimatter reactor before sealing off the tunnel, in order for him to match the correct greeble layout we see on screenin universe, Scotty is crawling deeper into the bowels of the ship, away from the hatch. On the set, it appears that Doohan is crawling back toward the hatch.
Note on the right hand side of this image (top to bottom): the dark bar behind the handrail, the groove, the single red pipe/stripe, the beige and silver cylinder, the yellow pipe, and the silver cylinder.
Scotty in the crawl way image
Compare those to the features we see when the hatch is open. If Doohan were sliding the same way on the set in both shots, we should see two red pipes/stripes and no dark bar instead.
Opening the hatch image
Was probably cheaper on the camera setup, etc, to do it that way.

EDIT: I see that Blssdwlf said pretty much the same thing already. YESTERDAY!!!
