For some time, I've noticed a trend for builders to locate their gps navigator (GTN650, etc) low - below the nominal panel over the center tunnel. I recently flew in an RV that was layed out like this. (necessary because 3 large glass panels took up all the useable normal panel space). I found using the 650 resulted in a lot of head-down time, and I mean really head-down. Not possible to make a quick eye-movement glance outside. It did not feel comfortable, even though I wasn't the pilot flying. In addition, since the glass did not display all of the 650's enunciations, this is a technical violation of the installation instructions, which are part of the TSO. I have observed, from the right seat, a pilot fail to notice a downgrade from LPV to LNAV, even though his 650 was within the specified mounting location. He did notice the GS had failed, but didn't follow thru to look at the GTN. I'm interested in others' opinions. Is this a real safety issue? A matter of needed training or awareness? Or is this a non-issue?