It Doesn’t hit the thumb screw, but did hit the tab cover, and wouldn’t let the seat to be removed wth the screw was taken out because the (wire tray???) held it down. With out the cover there is enough clearance to get the seat off.The part that I think you are referring to is the tray for the wires for the tour pak. But it still shouldn't have been moving to be able to hit the thumb screw.
I do have a detachable mount, that's why I needed a thumb screw because I swap out seats with the tour pak and mine doesn't come anywhere near the tab....but the detachable mount doesn't have the wire tray.
Just wanted to give a heads up to others so they don’t damage their fender with a inexpensive eBay part like I did.