I'm curious why remove the TV OTA antenna if it's functional? We get something like 70 HD channels, many good ones which not on DTV. Right now Starlink is still spotty depending where it is operated but still it is not the panacea and clumsy on television feed.You say TV unit, then say mount SL?
Why not just mount the SL on a 1" mount, possibly remove your TV antenna and use that mount. Very easy way to go. Do you have enough depth to flat mount? But to answer your question, that is a fairly large obstruction. I have mine in a similar location but only have a 1' dtv dome blocking. But that doesn't seem to interfere with it at all.