I shoot a lovely Merkel from time to time, of course. Over the thirty years i've owned, I've had a few days where it has bit my finger with that trigger guard.. And of course once that happens, it is done for quite a while. But the next time I pick it up. Everything is just fine and dandy. And I can shoot for a couple of years without it happening again. Obviously, I'm holding it wrong once in a while, and I pay a price for it..
If it is just a light tap I find, I can deal with it by either moving life. Middle finger way back so it doesn't get hit horror moving at waifu words. So it's pressing against the trigger guard.
The place it does not want to be is close to or barely touching the trigger guard well. I tend to lightly grip the gun, which is a bad habit of mine held over from rifle target shooting where my grip is intentionally the absolute minimum. With the shotgun, I think that kind of grip allows the gun to get up a head of steam before it hits my relatively stationary finger. If tightly gripped and pressed against the trigger guard, that doesn't seem to happen. Sort of like a rifle chamber with too much headspace, you don't want to let it get a head start.
Bow shape is probably also important, But I have never really looked closely at all my guns in a comparative fashion. I do not know that my six pound Cashmore That's never bitten me, yet I shoot down ounce and quarter pheasant loads in it on a regular basis.