IR from what?
I ask because you didn't give enough information about what you are doing. If you are testing with the factory remote, guess what... that is NOT IR. It is Bluetooth so it is going to work no matter what you cover.

If you are testing with an aftermarket IR remote, then you simply need to go around the bezel with the remote just an inch away, hitting the vol- command until you find the area it responds. Then narrow it down from there by using the tape to mask off areas.