May I suggest sitting up against the back wall, but bringing your speakers out from the front wall more than 1/3rd into the room? Also, with a fairly wide spread. This way you will have some sense of soundstaging behind the speaker plain.
You don't mention what direction the system is firing down, meaning the long or short wall. In a small room, and let's face it, with a smallish room like yours, every inch counts so let's make the most of it. If I had a small room, I would fire down the short wall and have the side walls as far away as I could as to take more the the side wall reflections out of the equation. So, maybe space your speakers parallel to the 13 foot side of the room, brought out more than 1/3rd into the room with your back up against the back wall. Just a thought...
You don't mention what direction the system is firing down, meaning the long or short wall. In a small room, and let's face it, with a smallish room like yours, every inch counts so let's make the most of it. If I had a small room, I would fire down the short wall and have the side walls as far away as I could as to take more the the side wall reflections out of the equation. So, maybe space your speakers parallel to the 13 foot side of the room, brought out more than 1/3rd into the room with your back up against the back wall. Just a thought...