As a quick and dirty method of fitting, try the following.
1 Unload and double check.
2 Position yourself in front of a mirror with enough clearance to point the shotgun at the mirror.
3 Practice a few mountings with the appropriate clothing you will be wearing when shooting. <--= IMPORTANT (winter and summer can need a change of pull length) It's why there are lots of movable triggers these days.
4 Close eyes and mount the shotgun pointing at the mirror. (If you break the mirror, it's not my fault.)
5 Open eyes and see how the bead(s) line up with your correct eye. (Do you see lots of barrel and then the bead? No bead in sight?)
6 Record the position of the alignment on paper from the shooters perspective. (eye to the left or right of bead(s), eye below or above or dead on the point of aim, do you see two beads? One bead superimposed on the other? Rear bead higher than the front? Front bead higher than the rear?
7 repeat without attempting to change anything, just keep the eyes closed and check eye alignment with the bead(s).
Proper cheek weld is important. This changes with individual facial configurations as well as all the stock measurements. I personally use what I refer to as a military style mount where my cheekbone rests on the comb of the stock and my face is as far forward as I can comfortably get. Consistency is the desired effect, when the gun comes to the same position all the time and you have a consistent bead position, then move forward with changing stuff. Make ONE CHANGE at a time and try it out.
People want the beads in different places according to the use of the shotgun. Trap shooters in general want the lower rear bead or a higher front one. It's a perspective thing and good on rising shots. I've heard skeet shooters like a figure eight for bead appearance. I never understood that since in one direction and the, the other, would present differing points of aim. To me, I like superimposed beads where the front one is just a bit larger than the rear. It's funny, I never see the beads on a shot, just the position of the target in relation to the beads. My concentration is on the target, not the gun.
Give this a try and report back on what you see for discussion as what to change.