I'm not sure if this is what Nefesis meant, but if you put the washer under the plexi, it could prevent the stick from pulling out to twist and change 4<->8, rendering it a plain old T-stick, and not a T-stick Plus anymore.
Because the ball tops don't have the spacer sleeve that the bat tops have they have a flange at the appropriate spacing on the shaft itself. The dust washer sits on that, and if you don't leave enough space for that flange to travel, your washer will block the whole reason for a t-plus.
If you're mounting it in wood, you should be fine, but metal or surface mountings would be bad with the plexi on top of the dust washer.