When you use "Create Polygon-circles" to create triangles, it is always the middle of the map. Any other way involves major calculation unless at least one connection between 2 circles is parallel to x or y axis.
If you insist you can always read the coordinates of the 3 corners here and calculate the position of the middle:
But that is a chore unless you have some kind of tool for that. Wolfram Alpha wasn't too eager to calculate that for me.