The 13 by 18 room would sound way better for your maggies set up on the 13 foot wall assuming you have two solid right angle corners in it.
Should I switch to a larger room?
My current listening room is 10x12. Since I live alone, I could make my master bedroom my dedicated listening room. It is 13x18. Switching rooms would be a PITA, but is it worth doing? My speakers are MMGs and they will be getting the Peter Gunn mod in the fall. I do have some room treatment from GIK Acoustics delivering in a few weeks, but what I ordered was based on my 10x12 room.