You'll notice that the triangular composition shots had three figures on three different levels in the shot, when most shots with a single figure in them had th

You'll notice that the triangular composition shots had three figures on three different levels in the shot, when most shots with a single figure in them had their head at basically the same level, right below the top of the frame. If the default placement for a character's head is near the top of the frame, it would indeed be a conscious choice when placing three head in a shot to make them at three different levels.