It's exactly what you think, the size between the two. It has the ribbon tweeter like the 3.7i but smaller. I heard it Saturday. It's excellent but it doesn't seem much smaller than the 3.7i.
Magnepan 2.7i
On the Magnepan website in the Floor Standing speaker section you can find a 2.7i. Not much detailed information on this speaker in the website. Does anyone have any more details on this one? I currently have a pair of 1.7i's and would like to get 3.7i's in the future but maybe the 2.7i is now something to look into?