If you can, the corner. You get the best bass response for the room that way. If not, then yeah, right up against a wall. And no, you don't have to have it up at ear height. Bass frequncies are very easy to get out into a room. The big question is how good they sound.

Also, it'd be a good idea to keep it in contact with the stage. This will make the entire stage act as a piezo-driven membrane, and help get your bass out there.
Sure, your singer will complain that you're in his mic, but he's a singer. Don't listen to him.
Rock on
Eric