I shot years ago with my index finger at the corner of my mouth. It was more comfortable as my thumb was under my jawbone, but it was mainly to clear those big "aviator" glasses, that were "styling" at the time, LMAO! If you gap shoot... Your gap will be increased dramatically, and your point on will probly be increased about 20yds or so. Shooting truely instinctive your sight picture will open up a bit. Nothing you can't get used to though!?
Last 10 years or so, I've been shooting middle finger, and going back & forth between split finger & 3under. Play around & see what's most comfortable for you...