Could this be related to the MSFS stop position updates or is there something else going on?
Yes, of course is related to it, because we assumed it was an improvement that should be valid for both simulators: before the update, the bigger the parking radius, the more the airplane was placed too far back, because the default method (lacking a custom Stop position) would place the reference point of the airplane in the center of the parking spot so, larger parking spots that, due to their size, were placed more behind, would result in planes, especially mid/small jets parking in large parking spots, to far from the jetway, so now there is a correction fact, of about 1/3 of the parking radius.
But that's just the default, when no better data is available. For best results, you were always supposed to customized the Stop position, and in this case, changes to how the default position is calculated, won't have any effect, since the customized Stop position is always used, when available.