CZ, I just measured a BPI X-Stream insert and it's 5/8" of an inch tall.
Even one ounce of shot covers it deeply in a 12 gauge shotcup. There's no need to cut it.
The Polywad insert can be loaded as you describe with some shot on top if you find it worth the effort. I don't. I'm not a believer in holes in patterns 'patchiness or voids' as O&T called them making any difference in the actual 3D world of shooting moving targets.
I knew a class AA trap shooter who used the PC post wad for 16 yard trap in a full choke 1100 for many years. If it caused holes, he wouldn't have been class AA.
