You answered your own question: it's your ball and your thumb. Do what feels comfortable and right to you. There is no right and wrong when feel enters the picture.

I never used rough white tape until I had to; ran out of black and had to borrow tape. I generally use it on the front of the hole where my thumb's pad touches the surface BUT I have also used it in the back when it was necessary.

You may be adjusting not only the general size but also adjusting the contour of your thumb hole to properly fit your thumb's shape. Everyone's thumb is different. Next time your friends or other bowlers tell you that you are wrong, ask them if their thumb is identical in shape to yours.
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"We get old too fast, and too late, smart."