I don't like to us the word comfortable, because sometimes a "comfortable" position is what we have learned and it is wrong. And, the rifle gets set up wrong in that position. Sometimes the "correct" position feels awkward at first, it did for me. Now, the right position is comfortable position is relaxed and correct. "Comfortable" was wrong for me.
Get in the correct position and then find where you are relaxed with no muscle tension. Relaxed is really what you are looking for because you want to be in a relaxed position to get in NPA faster. The more you can relax, the less you influence the rifle. Prone is the most relaxed position, because you can lay there and the ground supports you and the rifle...
So, for set up, you want to be in the correct position to manage recoil after you press the trigger. Being "comfortable" may be in the wrong position to manage recoil. Basically, its possible/likely your body doesn't know correct right now.
In short, bring the buttstock directly under your ear, on the collarbone, as close to the neck. Especially when your body is upright, bring the buttstock up so that you don't have to crane your neck down or forward. You don't want to crane or push your neck around.
Because you are shooting PRS, that is going to be your position for the majority of your shots. Set up your rifle buttstock in that position, is my suggestion.
Then, get prone, bring the rifle centered up to your neck. You will then see that compared to the upright position, your head is further forward.
Eye relief will be different for those two. Upright the scope will be slid further back. In prone the scope will be slid forward more. Pick a spot for your scope so that you have acceptable eye relief for both.
Go watch Phillip Velayo videos, Franks videos, and check out the Everyday Sniper podcasts and section in Sniper's Hide. They explain correct body position and rifle engagement.