If you wanted to get very accurate, you would need to find the shortest cutter and set the rear stop up for it, then file each remaining down until it touches the brass roller.
I've filed quite a bit with the FG2, found 0/30 and 0/25 works as good as 10/30 on most of the Stihl chain. To be honest, the only time I use the FG now is to try and even the cutters or angles. Most of my filing is done free hand while on the powerhead and starting to use Mike's chain vise. Free hand on the bar or in the vise is sooo much faster...