It gets a little tricky. But doable still in a rectangular room.
You can mix multipliers to compensate. Its not ideal, but can be improved upon with how the sidewalls are treated.
For example, if you want to shift right you can place at 0.2x width from right side and 0.32x width from left. The distance from the front wall should remain the same between speakers. The listener still need to be positioned at center wrt your R/L channels. The key is avoiding speakers and listeners in either a modal peak or null.
The "magic" multipliers are 0.2/0.32/0.45/0.55/0.68/0.8
Shifting from a fully symmetrical setup is detrimental for matched spl, timing cues and balanced imaging. But, you can compensate by measuring per channel spl at the listening position and adjusting for differing boundry reinforcement. Channels placed near openings or further from walls may need a db boost to compensate. Using a subwoofer(s) for low frequencies will reduce the differences in low frequency boundry effect. Timing cues can be fixed by reducing strong lateral reflections. Absorbtion at first reflection points is your best recourse.
