Which equates or replicates to you moving the binoculars up and down whilst observing a subject, not something I usually do when endeavouring to keep everything steady.
We all move our binoculars up and down, due to the Binos weight, their length and Gravity
The forehead is not a steady place in any way, maybe excepted in one horizontal direction ("maybe" because it's your neck muscles who can block your head).
But as the Binos shakes are mostly on a vertical axis rather than on a horizontal one, an horizontal block doesn't help (that's why a Finnstick helps).
Not even talking about the fact that eyes and forehead are not on the same vertical plane, so the "theoritical stability" of 3 points is doubtful.