Should also reduce the maximum speed, did you try that?
In my experience it doesn't significantly decrease the max-speed, if at all when u leave the small lens area completly free.
It doesn't affect the area of light the mouse tracks when sitting down anyway, just the area infront of where the sensor takes pictures of, which then would wander right under the sensor while lifting the mouse off.
But that gets cut of with the tape:
I have a Gigabyte GM-M6880 optical mouse. I have tried to put scotch on the entire hole but it reduced tracking completly. Then i put like you showed in the picture but depending how much of the hole i covered it either did nothing or it reduced tracking completly. Any suggestions?
Also why is non transparent tape essential? I've seen the same tutorial on youtube but many of them used clear tape.