I have the one on the palm at the base of the index finger. I'm told it's a good one (as in, a lot of good players havethe same callous). I don't find that it causes me any issues unless I go 6 months without bowling, where the callous disappears, which can cause blistering, which is less fun than it sounds.

Not sure about the callous on the tip of your index finger, my intuition would be that you're pressing too hard on the ball with that fingertip (which can give you a useful, subtle, reaction change). I tend to go for an even pressure with the whole finger, rather than just the tip, which should sort that callous out.
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Reporting from England