like is there kind of a set rule where your fingers should be in comparison to your palm, or should it be just what is comfortable to you?
it just depends on how big ur hand is. If u got a big hand and a thin grip, then you cant hold it tightly cause ur fingers are too long. In that case just buy thicker grips or overlap a few.
No hard or fast rules, but I would say too thin and you will be prone to injury, too thick and it will impair your racquet movement.