I lucked into the technique years back, just seemed to be able to do it, on anything i put my hands on (at least it's one thing on the guitar i can do well), so thats the baseline. Starting from there i can say that i get varying degrees of potency depending on the guitar. I would have said pickups, but i suspect the guitar itself has more to do with it. for example, you have a hard time not doing pinches on my axis. but they're definitely not as lively on my Mcarty Trem. The axis has dimarzio's and the Mcarty has a nailbomb, i have a hard time believing i wouldn't get the same squealy results from the axis if the Nailbomb was in there.