[bpape]

The 38% rule works in perfectly rigid rooms (there aren't any) just like calculating your room modes won't be perfect. Also, the 38% rule looks to keep you out of the lowest axial modes (length dimension). It does not, however, take into account the interaction of tangential (4 surfaces) and oblique (6 surfaces) modes.

Sometimes, where it best purely in terms of axial causes strong interactions from other modes which are more destructive. Normally, axials are about double the intensity of tangentials, which are double the intensity of obliques. So, axials usually dominate. However, if you fall into a place where you have multiple non-axial modes piling up, it can be very intense and needs to be considered.

Reader's Digest version - stay where you are - it works in your room.

Bryan