I didn't have the greatest experience with a Mighty Armory sizing die and it was pretty much due to what you described... after speaking with Wayne, well, let's just say that not everybody agrees on what exactly "cam over" actually means... when he says "cam over" I think he means torque the shell plate a little, like you'd do on a Dillon, screw down to the shell plate, then a little extra, doesn't really work like that on a single-stage, can't really flex a little steel shell holder much.
I had to remove materiel from the face of a shell holder in order to achieve a shoulder bump, but without access to a proper machine, I had to do it caveman style with sandpaper and a flat level surface, but you can't be off by more than a degree or few, or else all your rounds will come out leaning over like the Tower of Pisa and your brass is kinda all slightly fucked (ask me how I know, and I say only slightly fucked because it fire-forms out on the next firing, but taking a well cultivated batch of brass and "tweaking it" for a cycle is probably not the greatest if you can avoid it).
In the end I just went back to a known-quantity L.E. Wilson bushing die. IMHO Wayne is legit with his stuff when it comes to progressive press applications (like automated) and loading for pistols and semi-autos/gassers, but having talked to him, I got the sense that bolt-gun/single-stag/precision type stuff is not really his area of expertise.
Just sayin', I still like MA's stuff, just didn't work for me for the bolt gun. YMMV