There's only a one hard-and-fast rule:
Don't mount the detector behind any type of tint/windshield-treatment which is metallic in nature, and may attenuate or totally block the detector's receptive capabilities.
All of the other factors are really end-user preferences, and can be debated from both sides of the equation.
Those who say to mount high will say that this is the best position to capture "over the hill"-type signals, as well as the lucky scatter/reflection or "pass-through" from vehicles further down-road. Similarly, they cite that this close-to-the-headliner and often "behind tint" location can keep prying eyes away from the detector, as well as may somewhat lower the temperatures seen by the detector on hot summer days.
Those who oppose this type of thinking cite the fact that many detectors, when high-mounted on a higher greenhouse ratio or lower beltline vehicle may cause the detector to miss true LASER hits, as well as the fact that placing the detector so close to the headliner may limit the rearward view of its laser sensor or light-pipe, and that the tint, even if non-metallic, could also further reduce the sensitivity of the LASER sensor behind it.
Opponents of a low-mount, though, will say that there's virtually no benefit to be had by being sure that your vehicle has been hit with LIDAR (i.e. that the detector is simply warning you that you're getting hit with LASER, and thus informing you that a ticket is "on its way"), and that the dash or mid-windshield placement can make the detector all to visible for anyone looking in, as well as will "bake" the detector on hotter days.
And all that debate doesn't even include ancillary factors, such as whether or not the detector may intrude into your field-of-view, as well as what you prefer in terms of how you co-view the detector with the roadway, as well as tertiary considerations such as whether or not the detector's special features (such as "autosensitivity" of ambient brightness, and adjusting the display to compensate, which may be compromised when the detector's mounted too close to the headliner - or, alternatively, the acquisition [or acquisition speed] of a GPS-signal) may be affected.
The best you can do, wadecool
, is to simply educate yourself as to what the different mounting positions' compromises are, and what they will imply in terms of performance and your own unique end-user preferences, and set the detector to your