Mic positions do not literally correspond to seating positions. For example, you wouldn't want to measure a seating position that is far off axis because then Audyssey would "hear" a drop-off in high frequency response (being way off-axis from the speakers) and would boost them to compensate. Mic positioning is well covered in the FAQ/101 guide.
I just bought a theater type recliner and I have it a few feet away from my couch and further from the system, but dead center (Sweet spot). The couch is off center of the viewing area but the last seat on the right of the couch sounds great!! I then move over to the new chair a few feet away in the zone and it sounds flat? I was thinking if I miked the chair as my main seating position, I would get a better response. I guess it probably has something to do with distance??
I'm not really sure what you are asking. If you have introduced an additional seat into your room, then you need to run Audyssey again anyway simply because the new seat will have changed the acoustic characteristics of the room. When you run Audyssey again, follow the advice in the FAQ with regard to where you position the mic. These specific questions and answers may be useful to you: