You put tape wherever you have to in order to achieve a good fit.  Stop over-thinking it.  Do what you have to do to get a good thumb feel and don't worry what others are doing.

Really.  You asked, I answered. 

Simply put, your pro shop operator is a neanderthal. Tape is all personal preference, no ”right” or ”wrong” answer.

I usually try to go one in the front and then one in the back.  But it is just preference to whatever feels good for you.  I would guess the proshop person said that because maybe the textured tape in the back of the thumb hole could tear your skin.  That is the only thing I can think of.

I usually put about 3-4 pieces of the white (textured) tape in the front of the thumbhole in the winter and down to 0-1 pieces in the summer.

Occasionally---usually sometime in the winter---my thumb starts to slip out of some balls premturely, no matter how much tape I add.  Out of desperation I will then remove 2 pieces of tape from the front of the hole and add one piece to the back of it.  And it works like magic.....for awhile.

Sometimes one or more games, sometimes for 2-3 weeks.  Eventually, my thumb feels like it's hanging and I remove the tape from the back of the thumbholes.

Never left the tape in in the back of the hole long enough to seriously tear up the back of my thumb, but I suspect that over time the skin gets rougher and this is why the ball starts to feel like it's hanging.

I have also heard from time to time that you should never put the white textured tape at the back of the thumbhole. I think it's just personal preference myself.

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I would guess the proshop person said that because maybe the textured tape in the back of the thumb hole could tear your skin.

Then you can put Franken Tape from Valentino Bowling on top of the textured tape to protect your skin from tearing.  It's very thin and works great...

Franken Tape is great tape. I always did what you suggest with the Franken Tape before switching To Magic Carpet about 18 months ago.