One other thought... Does the bobbin go in the same way on both machines? My Bernina and Elna both have the thread go opposite the way it finally comes out, but when I did the ex's machine (a Singer) that way for my daughter one evening, what a mess it made.
On the Elna, the only time I got lots of top thead living below the plate was when I was using crappy thread and it filled up the bobbin area with fuzz, making everything go Kafloooy (highly technical term).
tim in san jose