You're speakers are on the best wall and your room dimensions are pretty good but an extra foot or two to make it 13.5' x 18 would be even better.
Go to cardas.com and look for golden room optimal speaker placement type stuff.
My room is 12.5 by 18. The speakers are 5.5 ft from the center of the woofer to the back wall. They are approx. 2.9 ft from the side walls to the center of the woofers.
Sounds like you just need to bring the speakers further into the room and away from the back wall by a couple of feet.
Once you zero in on good soundstaging, etc., you then should play around for the next few weeks moving the speakers an inch at a time in different directions to find the optimal placement.
Also, consider a slight toe-in where the speakers are actually pointing directly toward the outside of your ears from your listening position. This will help minimize initial reflections from the side walls nearest the speakers.
Go to cardas.com and look for golden room optimal speaker placement type stuff.
My room is 12.5 by 18. The speakers are 5.5 ft from the center of the woofer to the back wall. They are approx. 2.9 ft from the side walls to the center of the woofers.
Sounds like you just need to bring the speakers further into the room and away from the back wall by a couple of feet.
Once you zero in on good soundstaging, etc., you then should play around for the next few weeks moving the speakers an inch at a time in different directions to find the optimal placement.
Also, consider a slight toe-in where the speakers are actually pointing directly toward the outside of your ears from your listening position. This will help minimize initial reflections from the side walls nearest the speakers.