Some suggestions, as I just went through a similar scenario myself. disconnect one of the subs, and take individual sub measurements at all of your possible locations. REW has an option in the controls window that lets you do an A+B summation between two measurements. This is quite accurate, and will let you preview which combination of locations might work best together. Don’t forget to try multiple facing directions at your best locations, as it can make a bit of difference. Keep in mind, with dual subs, a flat frequency response pre-audyssey matters less than avoiding nulls. If you have a huge boost in one spot, audyssey can fix that, just not the nulls, as you’ve discovered.