I’m assuming trigger grip is like what I call Curl Grip in some of my books. That’s where the pick is held with the side of the index somewhere along the first joint and the pad of the thumb. In that grip, it’s quite natural for the fingers to roll up in a soft fist (hence curl grip), like Gilbert, Di Meola etc. Great all-round pick grip for different escape paths and whatnot.
The grip you’re referring to in my playing is what I call the LAX grip (as in, reLAXed). There’s more pad of the thumb meets pad of the index. Not full pad to pad contact because that would theoretically put the pick in another pick edge offset.
When there’s that crossover point of finger-side and finger-pad, the other fingers open up (at least for many of us) - like the Yngwie pick grip where the fingers chill out on the pickguard without overtly pressing into it.
Wait, here’s a pic. Hopefully I can post it inline right here…
That’s what I use for the Yngwie stuff. Like the right pairing of wine and cheese, I find it really suits the upward escape path and wrist + forearm motions.
If your index finger is hitting the string, maybe it’s a small pick or you’re gripping too close to the tip? See if you have the regular fender/dunlop shape pick and see if it makes a difference. For a very small pick, you might need to sit back quite a bit or experiment with the other grip above. It does straighten the finger out comparatively to the curl grip, so I understand than pitfall. The well-worn angle of my index fingernail confirms that!
Either way, the curl grip (if that’s the same thing as trigger grip) is still plenty fine for playing that Yngwie material. You just have to ensure with hand positioning optimises the upward escape path. I’m sure the Pickslant Primer will cover this in much more detail than I can type here.
Here’s a pic of that too for visual reference (at least my version of it).