How do you set up your bench to avoid "shooter's shoulder"?

My guess is that your bending over the gun 'too much'. Try putting a piece of scrap 1 x6 or 2x6 under the front bag and see if that helps. 

Sounds like you need to adjust the height of the front rest. You could buy a adjustable Caldwell. If you want to use what ya have...….position yourself with your head near vertical and elbow on a thin pad and get nice and comfy...…..do whatever low tech you can to position your Caldwell bag to fit your desired body/comfy position. Once you find what fits, you can "jury rig" something to put under the Caldwell that can be used in the future.

I like Caldwell stuff and have a threaded rod front rest with tri-pod pointed ,no slip steel feet. Works great. Easy to spin wheel for height adjustments.

I hope ya get something you like. No fun being uncomfortable while having fun. You will get it figured out and it's all good.

I use a plastic folding table and a outdoor/patio chair to shoot off and use an Atlas bipod and rear bag. The bipod has enough adjustable height to shoot comfortably. 

2 folding saw horses I bought at the Big Box store, 3/4" plywood cut to fit inside the back of my Cherokee, old OD army blanket, and a thick hunting sock filled with the cheapest white rice I could find on the shelf. Stack books 'till I'm comfortable with the sock on top. forearm on the sock, butt pad on my shoulder. This is an old pic before I started using the sock.