It was never brought up again. Fans speculated that the variable geometry was the fix, but Voyager never addresses it, and it's just as likely it's done to give Voyager it's superior warp speed.
Looks like Memory Alpha says you're mostly right! Apparently it was never mentioned on the show proper as the reason for the variable geometry, though it shows up in some of the tech manual stuff that I think isn't considered canon? I wonder if that's where I got the notion.