A few things to help you get these sounding better and flatter.
First, you're definitely on the right track by deciding to turn off Audyssey and run REW during the sub crawl. May I also recommend to use no smoothing in all your REW sweeps - this will not only help you see the nuanced differences between positions, but also it prevents frequency anomalies from sneaking in without you seeing them.
Secondly, if you haven't been already, make sure that in REW, each new measurement you take gets labeled with positioning info so you can return to that position later & repeat the measurement(s) to verify.
Third, increase the volume on your AVR so that your sweeps aren't impacted by any outside factors. Starting at 90-100dB sweeps will help avoid this. If you do this, you'll prolly want to wear ear plugs. Also, do all of this with the program select button pressed IN. You'll change this later. You can also change the measurements results window to only show the region you're actively measuring - from 5-80Hz.
Lastly, trying odd combinations of positions may work, but also remember that you likely want to find the best response before Audyssey AND you want that position to actually work for you in your day-to-day life.
A few notable positions to try:
Opposite corners up front
Both on opposite middle of side walls
One up front and center, other opposite side middle wall.
Your third is going to really tie the room together, so keep that in mind. Potential best spot will be one up front & center, other two mid side walls, but that varies by room.
If you're lucky, you'll be able to get something like this with the above positioning and no EQ:
Then, once you've found the best spot, re-run Audyssey with the program select button on the Speakerpower amp pushed in. Once it's done, re-measure. If you're satisfied with the results, let the program select button out and proceed to victory over your room!
Best of luck.