How would the cylinder sub being in the corner behind a couch sound. I have never heard a cylinder sub so would one like that syle be ok behind a couch?
The shape of the sub doesn't change the sound of it assuming its insides are well dampened and internal standing waves aren't an issue.
The problem is, your room. Bass frequencies may leave the sub uniformly, but as soon as they hit your walls, they're going to change in direction, intensity, and clarity. You'll find that at your sitting spot, different subwoofer placements can give you completely different sounds. On that note, sometimes it's better to get a cheaper, or a pair of cheaper subs, and leave some money in the budget for some corner bass traps.
you can have a 3000 dollar subwoofer and have it sound completely boomy and awful if you stick it in the wrong place. The only way to know the best place to place it is to play around with it once you get it. You may even find that rearranging everything in your room is worth it.