It has never occurred to me that people use three fingers on a mouse. I'm using a Logitech M705 at the moment. If I put three fingers on this thing they just don't fit. The finger in the middle covers the scroll wheel and at least 1/3 of each of the other two buttons.
The side fingers naturally land on the side of the mouse on the seam between the mouse body and the buttons.
When holding this mouse normally with two fingers the scroll wheel disappears in my hand.
I haven't found anybody we makes mice big enough for my hands.
I suspect there are a lot of people who have the same issues.