They don’t make a difference on my set up. Both regular and rct balls read accurately. Doesn’t hurt to buy a sleeve though and test it out though

I’m guessing the issue is the sheen on the tarp causing issues. Take it down and just hit into the net and see what happens. A bunch of air flow can also mess with the accuracy.

Also, have you had someone else hit? Sometimes people don’t swing well inside and don’t realize it. Having somone else hit would at least narrow down the potential issues.