I see sudden signal level drop between 6295 and 6300 MHz. Latest response from support (after a few back-and-forth to upgrade RouterOS and try various settings, with not much effect):
"The output power and the receive sensitivity can vary on the upper frequencies and there is nothing we could do about that as that all is happening inside the wireless chipset."
It's very disappointing, in my opinion if the product is advertised for the range 5.9-6.4 GHz then it should work well over the whole range. I did expect some variation, but it is common practice to specify frequency range at -3 dB loss, not about -20 dB which I see here (about -73 dBm signal on a 750m link between two SXT6's at 6375 MHz).
I was hoping for a 3km link between SXT6 (AP) and DynaDish6 (STA) but below -80 dBm it is just unusable at the frequencies available to me (near end of the range).
Has anyone looked inside, if the product really operates the wireless chipset directly at such high (out of spec) frequencies? I would expect to see some up/down-conversion circuits inside, perhaps the change at 6300 MHz has something to do with frequency range switching.