Mounting high is bad for laser, so if that is a concern for you, then yeah, I wouldn't put it high. Though if laser was a concern for me, I'd have a jammer.
And everything they said about mounting it in the center had nothing to do with making sure the detector is getting the best range as possible and just stuff about laws, not attracting attention. These aren't of concern to me, though of course, if that stuff matters to you, then don't put it in the center.
I use my detector in three cars, so I don't have mine mounted very high because of wiring, but it's higher than many people have their's and it is in the center.
You want it high enough that it has a decent rear view. You don't want to block the rear facing part of the detector with the car's seats or whatnot.
And a good radar detector isn't going to false very much anyways, so that's not really a big factor when it comes to mounting position for me.
And I don't appreciate being told I need to slow down.