Ever had problems with your mask being knocked off in a game? Does your mask leak when the skirt rides over your cap?
Years ago this was a big problem for me. Guys in my team including me were experimenting with different kinds of mask straps, and building their own custom straps that were bomb-proof and ratcheted the mask so tight on your head it'd survive a nuke, involving bits of hosing, plastic clips and seat-belt nylon. It was a crazy time. When I was a young fella I heard tales of masks and headgear being ripped right off in test-matches and guys duct-taping everything that could be removed to themselves to prevent it. Funny to think back on.
Then one day I was visiting in Holland and putting my gear on poolside for a club practice, standing next to Sandor Duis. He asked me, "why do you put your mask on over your cap?" I shrugged, said "I dunno, I always have?" And I tried putting my mask on the way he did it, under the cap (which looked weird to me). I have never ever had a problem with my mask being knocked off in a game again (apart from when people do it on purpose of course).
No fancy webbing straps, just the standard silicon from the factory. Once you get used to it, it's easy to adjust the strap on the back of your head through the cap if it slips down to your ears. When your snorkel or cap gets knocked or pulled out of your mouth, or you get crunched, your mask hardly slips even if the cap pulls off. Just clear it underwater and carry on. Compare that to having your mask over the cap... any yank on your snorkel pulls your cap and mask clear around your head and leaves you gasping on the surface like a blindfolded mummy.
Many people will just nod and say "of course, why would you do it any other way?" But I still see lots of players with fancy bomb-proof buckles and straps on their masks on poolside... and the vast majority of people I see around my local pools put their masks on over their caps. Sometimes I mention that they might try it the other way around, but they don't trust me like I trusted Sandor :)
If your mask getting banged around your face is a big problem for you and you haven't found another solution, maybe try the simplest solution in the book and see if it works for you?