Does it have positive or negative pitch? Measure it against the wall. Take two of your guns which fit well and measure them. Pitch is not super critical like lop, cast or drop at comb but you need it to be close. If your pitch is off easy way to alter it for fitting is to back off the screw in the recoil pad and place a spacer, I use quarters under the pad. Check to see if it feels/fits better. Quick, easy and reversible.
I suspect your new gun has less pitch than you're use to, if you feel the gun slide down the shoulder and the poi is higher than expected it should be too negative. If your poi is low it slides up your shoulder you have too much positive pitch. Perfect for you is the pitch which gives you recoil directly back towards the shoulder. Most of us seem to do better with a little positive pitch but now that I've said that there will be twenty guys who swear that negative pitch is the only way to go. And for live birds it might be better.
Unless way off norm I look at poi to see if I can shoot a gun with its current amount of pitch. But a 1/8 change in the recoil pad may be nearly an inch pitch change.
