I commonly hear that distance from the wall can be as little as twice the port diameter. For some reason, I am thinking the cantons port is downfiring? Dunno how that affects that metric. Regardless, I think 12" from wall is good, but you could try it closer, no less than 6."
More than anything, I would try to make certain your ears are 1/5 the depth of the room from the back wall. In that 12' space, I would sit about 2.5' (30") from the back wall.
Regarding seating and speaker distance, I am a proponent for an Isosceles Triangle where you are slightly further away than the distance-on-center between the two speakers. I know well that others insist on an Equilateral Triangle.
For me, the kicker is that engineers sit like that in an Equilateral set up because it emphasizes the Stereo Separation. This is an absolute necessity when producing and mixing a recording. When you step back from that Equilateral arrangement, you allow the stereo image to blend into a more complete whole.
Following that, my situation in an 11x15' room is that my speakers are ~6' apart on center, I sit about 7' back. The Terminus (ports) are 13 and 15" off the front wall and each speaker is ~30" from the side walls. My ears are about 4.5' off the back wall.
This is
not to say you
MUST follow my setup advice, rather to give you a different view of the
possibilities. I do run, currently, 7 channels, hence why I need extra space behind me. If I were just pursuing Stereo listening, I would move back another 1.5'.