tungsten exposure question

for tig, any rule-of-thumb for setting the tungsten protrusion length past the end of the cup.

for dc work, i have 1/16, 3/32, 1/8 tungstens.... i sharpen them to a nice pencil point and i keep just the pencil point outside the cup. so, the bigger tungstens have longer points, so they protrude more than the smaller tungstens.

i have also been using the same argon flow setting for all my dc work ranging from 20A to 110A.

what abou AC work. the tungstens ball up, so how far beyond the cup should the ball be ?

thanks for any info.