I have a large room 20x20 with 11 feet cathedral ceiling open into another space. My Triton 2's are 9 feet apart 39" from rear wall and 27" from side walls. Subs are set at 2 O'Clock position. Mains set to large,2 ch. mode on Rcvr. running speaker wire only. What is the recommended best distances from rear and side walls to increase bass response?

Moving the speakers closer to boundaries will typically yield more bass output. You can place them as close as 12-18" from back and side walls, toed-in toward the center listening area.

Is that 12- to 18 inches from the wall to the back or front of the speaker?

12-18" from the back of the speaker to the back wall, 12-18 inches from the side of the speaker to the side wall.