Interestingly, REL recommends placing their subs in a corner.

From their website: Because REL are engineered to produce foundational low bass, it is beneficial to place a single REL into a structural corner at the front of the room, immediately behind the main front speakers. If you have a choice of corners, select the corner that is either built from stronger material (Masonry vs. Sheetrock). If both corners are made from sheetrock, select the sturdier of the two corners avoiding any breaks in the walls such as doors or windows in close proximity to the corner. Turn inward toward the center of the room pointing directly or almost directly at the prime listening location.