Actually it should be quite simple! If each person is at a vertex and in love with all the people at vertices directy connected to it by an edge, then four people in a love tetrahedron are in complete harmony - each loves the other three!
Sure, sure, if we're talking geometry and cold logic... However, if we are talking about reading experience, may I direct you again to the gif in my earlier post?
I've heard the rumor about Anthony Astor/Muriel Wills somewhere before but there is nothing in the Henderson bio about any interaction between Tey and Christie. Tey and Sayers met, but apparently Sayers was unimpressed. I dare say, Sayers would not have been Tey's cuppa either.
Hmm. Her being unpopular with both Christie and Sayers would explain (inter alia) why she was not a member of the Detection Club -- though of course, she never bothered to play by those rules in her mysteries, either (especially not in "Brat Farrar").
http://brokentune.booklikes.com/post/1949284/reading-progress-update-i-ve-read-83