I suspect the answer will be simply, what ever you feel comfortable with.
For me, I wouldn't want my fingers right into the end of the cups, just to give you a bit of 'suspension' when you get hit, but fairly close. You don't want the gloves so tight that they make it difficult to keep your hands relaxed, equally you don't want them so loose you can't wrap the glove around the ball. Is use the padded chamois inners that match my gloves, I wet them slightly before using them as I (maybe wrongly) think they have more friction with the inside of the actual glove to stay put.
If you are between sizes in one brand maybe look at different ones, if you haven't already.