why go against REL setup recommendation?

I own a REL strata3, and corner placement resulted in boomy bloated bass, and lots of it. Mine actually sounds best placed between the main speakers, nearer the right channel. That's not to say that corner placement cannot work, but in my case it sounded awful. I experimented with spikes and without spikes. It sounded better without spikes, much to my surprise.

And FYI my crossover is set at 27Hz ... hardly midbass, so I think Sugarbrie's assertion that low frequency rolloff allows it to work in the corner is not always true.

I think you'll have to experiment as there are no hard and fast rules. However, once it's placed correctly and dialed in it's a great sub, and really adds to the music.

My experience was that the sub sounded terrible in the corner, no matter how it was adjusted. Since I have a 8x10 listening room (spare bedroom) I really would have liked it to be in the corner, but now I choose to step around it ... it's really in the way, but it sounds fabulous. If I had to run it in the corner I would have sold it ... it was really that bad. I would buy with an option to return if I was not sure that I could get away with placing in the middle of the room.

There's no one right place for a sub, but I have found that subs are even more finicky than the mains in terms of placement, to the point that if they're not placed correctly you're better off without one. Bear in mind when deciding to buy one, especially an expensive one.