When I was shooting field archery, I adjusted everything till my point-on was 50 yards and I had my gaps figured off of that. Anything 30 yards and under, the gaps were so big they were practically useless, so I shot those distances 'instinctive'. The gaps really helped put me on target from 40 yards on out.
I know exactly what you mean about that, my point on is at 40 yards, and I can gap shoot to about 30 yards. 25 and under is most definetely instinctive (well, Ferguson's become the arrow method). At 10 yards the gap is so large that it would impossible to gap shoot.
As far as the arrows, according to the Eason Legacy Chart, my sizes were 2018,2117,2020. 2018 worked the best for me.