Years ago.... (1970s)
I wore glasses with big "aviator" style lenses. I always anchored my index finger at the corner of my mouth.
I shot that way with a compound, and when I got back into this "traditional" thing around 2000.
I switched to 3under as a way to get my arrow up under my eye...
In 2015 when I got my Bear T/D I set it up for 3under, and it was LOUD!!!!
I dropped my nock point to 1/2" and switched back to split finger.
New glasses, with smaller lenses (and practice!) allowed me to move my anchor up, to my middle finger at the corner of my mouth. I've been shooting that way ever since...