Grabbing a handful of front brake while still somewhat on the gas could only make you highside if you grabbed just enough to maintain traction, while slow the bike enough that the drive on the rear wheel caused the rear to spin. The rear would then have to drift out of line with the front, then regain traction, snap back, and throw you off. Not likely, but I can understand why you’d want to be cautious. Highsiding doesn’t look like much fun, and like you, I do my best to avoid it
One thing I’ll say is that, like you would using four fingers, you still have to roll the gas off to get on the brakes when using two. The reason is that with your wrist rotated for the throttle, your fingers probably won’t be long enough to actually squeeze the lever without rolling back.
This suggests to me that you’re raising your throttle hand position when trying the two-finger method. Consciously return to a low throttle grip and then give it a try, just standing still, and see if that makes a difference. Just a thought. There’s nothing terrible about four-finger braking, so if it doesn’t suit you, don’t sweat it.