How many pounds is it, normally pre-loaded on headset bearings, just 8 or 10 right? So the difference with "slightly more" is some fraction of that. A few pounds, maybe less.

It makes me wonder if the weight we put on the bars, combined with flex in the fork and steer tube and angle thereof, cause less load on the rear top bearings than on the front bottom bearings. IF the fretting is exacerbated by preload pressure, then that might account for it being worse in the lower stack of bearings.