The max you would go to is the 20.7? That model IS the max Magnepan, except for the new 4-panel 30.7. I don’t recall what size room Elizabeth has her pair of 20.7 in, but 12’ x 16’ may not be big enough for the 3.7, let alone the 20.7. Either would need to be on the short wall, firing down the 16’ room length. Assuming you place each 18"-wide 3.7 panel 1’ from the side walls, that would put the inside edges of the panels only 7’ apart. Being only 1’ from the side walls, the tweeters would need to be on the inside, making the left-to-right tweeter separation about 6’---not much.
Have you seen the 20.7 in person? They are HUGE! They would absolutely dominate if not overpower a 12’ x 16’ room, but then so would the 3.7. The 1.7 would look more room size-appropriate, as would the similarly-sized Eminent Technology LFT-8b.