May be a personal preference thing, but in regards to modding a cap, IMO having the 2 prongs at 1:30 and 7:30 (...for right handers, 10:30 and 4:30 for lefties) is better than at 12:00 and 6:00. Having the prongs lined up straight vertical looks good in a "product showroom" sort of way, but having them lined up diagonally is more utilitarian, as it gives you the best visual window while working.
YMMV of course, depending on where you hold your head in relation to the brush (or vise-versa) while painting. Regardless of your own typical viewing angle, IMO you'd ideally want to match the orientation of the prong gap to that rather than just going for symmetry appeal.