PPatch, for me the best aim point seems to be different with different kinds of targets. Buy this I mean that I prefer a dead on hold for hunting but target work is different for me. For target work I always preferred the "six o'clock" hold that you describe. That works well for me on conventional bulls eye style targets, but not for non conventional style targets, like Hafner, novelty, or primitive targets. It may just be me, but using the six o'clock hold I have trouble determining just where to hold on those targets. Consequently, for consistency, I've recently started adjusting my hold for all shooting to dead on to see how that works out.
I shoot ML off hand at 100 yards or less; that's about my limit off hand. However, I shoot a Swedish M96 Mauser in old ordnance rifle matches at 200 and 300 yards and I find the same as you do at those distances. Once you get out to 200, 600, 1000 yards you had better be using a sight picture with the sights leveled at the bottom of the target because you simply will not be able to effectively, visually, bisect that bulls eye by holding in the middle.