Yeah, I really can’t argue with that. More speaker movement planned, but there’s probably only so much i can do.
So it is not that often where the speakers are sitting at a 60Hz null which is causing the 6dB dip. It would be much more often that your listening position is where the 60Hz null is which is causing the dip.
This is why usually, it's always recommended as GroovySauce said, to move the listening position first, instead of moving the speakers. Moreover, unless your speakers are on wheels, it's harder to move the speakers around.
The best thing to do is actually not to move anything first. Since you already have REW & a microphone, you should actually look at the possible positions you can put your listening seat. And then measure the frequency response of the listening position say 6" forward, 6" back 12" forward, 12" back, etc at ear level. Wherever you found the bass to be smoothest by looking at the graph in REW is where you want to move the sofa to.
Once you moved the listening position, you'll have to toe in and out of the speakers to make sure the midrange and treble balance and imaging remains the same as before.
Of course, if you have speakers on wheels, then it's relatively easy for you to afterwards keep the microphone now at the new listening position and then move the speakers forward and backwards by 6" at a time and see where the bass is smoothest. Once you've settled on that, you'll have to once again re-toe in and out the speakers until the imaging and midrange/treble balance is restored. I found that even though you can do the latter with the microphone too, it usually is much easier just to do it by ear. And then you can put the spikes/feet back onto your speakers.
In the past, I've found it impossible to determine bass peaks and nulls by ear since I'm not a seasoned pro with decades of experience. So I always use REW or other forms of RTA for that.