From what I've read in a CWNA training book: You want your antennas to all be the same direction. Because some laptops may use internal antennas on the upper half, with the screen, and because screens are normally vertical, you want all antennas to be vertical. If you have sideways antennas, it causes polarity issues which degrades the signal significantly.
Therefore, having the antennas higher or lower would mean non-horizontal communications, which are non-perpendicular to the antennas, and are less than ideal. If you mount a receiver on the ceiling, with antennas pointing down (instead of up), that's still vertical, which is desirably perpendicular to the horizontal airwaves sent out by other vertical antennas.
If you can't have your receiver be mid-height, then higher is probably better than lower, just because of the likelihood of less interference/blockage from objects. Of course, that is just a generalization, and is likely to be false if there is a reason why higher is bad (like being closer to another source of interference).
Wireless can be a funny thing, due to factors like changing technology, improving standards, and changes that can be made to an environment (like new sources of radio interference, or new furniture that suddenly has an unplanned impact on airwaves). Any specific advice (like whether higher or lower is better) is probably prone to not work well in some circumstances. So if you try something specific, and it's working well, I would run with that.
You do want link. So a higher link score is probably a good idea.
I just read recently that some of the settings that people used to tinker with (power levels), for older equipment, are not typically supported by the newer equipment. As new technology comes out, perhaps especially with newer standards (like 802.11ac vs. 802.11n), any rules that are given are probably subject to change. If your driver gives you a "link score", I would be inclined to trust that as the best simple advice you're going to get.
Higher is generally better because it typically avoids more obstructions. However it is important to understand antenna characteristics. For example, if your device has patch antennas, setting it "normally" on a higher shelf may put your devices below it and out of the primary coverage pattern. if it is near the ceiling, you may have to "turn it over" to get better signal. – YLearn – 2015-12-15T21:06:20.237
1Actual performance is always better then theoretical performance. I don't see the question to be honest. You do actual performance testing, you have some pretty clear results, the lower location is the best location based on the actual numbers. Without knowing the sources that say otherwise I can't comment on anything else. – Ramhound – 2014-04-12T09:24:35.263
@Ramhound: That is true. I was just wondering why is the exact opposite happening. – Anton – 2014-04-13T09:50:54.050