If you are running GIK soffit traps, you really can't do better than that for the corners. Spread the love around with mondo traps in between though!
Also consider EQ as a better option if your problem is more broad band and not really a room mode.
Electronic Bass Trap Experience
Does anyone have any positive experience with the PSI AVAA C20 Absorber? Probably would need at least two. I prefer not to stuff more boxes and tubes into the room. I have all 4 corners of a symmetrical room (425 s.f., vaulted A frame 7-13ft) treated with 16” square rectangular tower traps but need a bit more management for the 40-80Hz octave. Thank you, Dave H