Yes, I realized later on last night that shoot, another sub isn't going to help the nulls higher than 60 Hz.

I actually did figure out that I have suitable locations at 1/2 the distance along the longest walls that might work.

My nulls might look worse than normal, because ETF is actually testing every 1.46 Hz or so. Much finer resolution than a 1/6 octave test disc for example.

One thing I will report back on: this was a 2.1 test. Both L & R and the sub firing. I need to do L & sub, then R & sub separately. Maybe I'm getting some comb filtering between the mains.

If this helps, I'm using Vandersteen's suggestion for sub and seating placement. (Even though I have Mirage's now. ) He says: start at thirds. Seating 2/3 back from the front wall, and speakers 1/3. That's too far into my room, and he goes on to say, you can also use 1/5, 1/7, etc. I'm at 1/7 for the speakers.