Like holding a beer can in your hand type grip/pressure?
None....zero.
My thumb exerts no grip pressure at all. My shoulder, bag, and bipod are holding the rifle.
Middle, ring, and pinky fingers are either maintaining some pulling force rearward to maintain rifle somewhat in the shoulder pocket or used to position the trigger finger properly. Kinda depends on just how well you have NPOA setup with the bipod and bag. (Note grip/hand position is basically the same no matter what type of position).
Your support hand is running the rear bag to aid in position of the buttstock as well and make minor aiming adjustments by squeezing the bag.
View attachment 8458824
An
actual benchrest setup.....I've watched the shooter barely shoulder the rifle (mostly because the rules mandate it perhaps) and not have the firing hand at all touching the rifle. Commonly referred to as free recoiling the rifle. Their guns are much more mechanically supported and usually weigh much more to allow for it. The rifle will slide on rests under recoil and then pushed forward back to its initial firing position.
My eye to cheekbone spacing is very small compared to many people. Most people can't look through my setup. I like a comfortable bone on stock fitment myself for consistency. I don't use a light contact...barely there on the gun head position. I'm not crushing my face onto the stock. It's just resting there....eye is comfortably looking through the center of the optic. Not peaking up and in or crushed down and in. It shouldn't feel like chore to maintain sight picture. It's just right there when the gun fits you.