Counter quote from one of the sources he lists:
Can I mount my detector on my sun visor?
We generally do not recommend mounting detectors on the sun visor because the dark tint at the top of most windshields significantly reduces laser detection range, and the GPS-powered features of the Passport 9500i will not function if satellite reception is blocked. So, we do not include a visor mount as a standard accessory. While not recommended, we do offer an optional visor mount that can be seen by clicking this visor clip link.
As a rule of thumb, a lower detector mounting position is better for laser and a higher position is better for radar. But, in most vehicles, the difference in height between the top and bottom of the windshield is not enough to make any perceptible difference in radar reception. It's best to mount your detector where it has a clear field of view front and rear (plus a clear view of the sky for the Passport 9500i), and where you can see it without obstructing your own view of the road.
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The point I was making about the Valentine possibly working better lower and forward for side detection was due to the curvature of the windshield in order to have as good of a side view as possible. The higher you are it would seem the more you could have obstruction by the windshield pillars.
The comment about what would occur from the rear is that glass will affect what path the microwaves and laser for that matter takes due to angle. I really haven't seen any real studies on this for autos but have seen some for communication systems such as transmission through windows in residences.
The ideal solution is to not shooting through the glass at all with externally mounted sensors. I have heard of some issues with glass in certain types of cars, if I remember correctly BMW (maybe Porsche) may have a coating where this can be an issue.
Perry