I came upon a relationship in which natally Person A has a T-Square:
Moon(Leo) in the 11th house oppose Jupiter(Aquarius) in the 5th house
both square Pluto(Scorpio) in the 2nd house
Person B has Moon(Taurus) afflicting all the above planets, basically completing Person A's T-Square and creating a synastric Grand Cross.
So far, in observation, I have not seen a great deal of conflict. Indeed as to be expected, the natives are very fixed in their beliefs and come into conflict with each other if either should try to control the other in any manner. They seem to encourage each other to achieve the best they can at whatever they do. The T-Square native in particular seems to be the spur to get the Moon, pushing them to achieve their ambitions. While the Moon native seems to be the means of exposing the latter to occult influences and helping them think outside the box.
My interest is to know what others may have observed with such a combination (when another native fills in the missing leg of a T-Square with a planet), if ever they have encountered it.