That's the same observation here and it's not a basis to conclude that the router is transmitting with a lower power because when I change the router's orientation 90 degree from the original position, the signals from this firmware is as good as Merlin's .270 based drivers. It's might as well be good only for my environment but it's a good thing to try just in case.
I don't really believe this is a workable fix for me. With the SDK5 drivers, I was getting -65 dBM in my back room and with SDK6 based drivers I get -90 and my devices in that area (Android tablet and security cameras) have intermittent dropouts. Rotating it 90 degrees, even if it fixed the problem in that area, would likely create new problems in other areas. I'm measuring a massive drop in signal quality ALL over the house, regardless of position, with SDK6 so router positioning is nothing but a single-position-based bandaid IMO.
I think the proof that there is something wrong is that, as previously pointed out, setting the signal level on the professional page has absolutely no effect regardless of what you set it to in the SDK6 releases. It worked in the SDK5 releases. So it's like something is hardcoded at a much lower signal strength on the newer releases.
Mike