Isn't two dimensional thinking good enough? Place a ruler on a white key and measure from the tip to the pivot point.
Of course there's always some room for nitpicking.
For example the keys are not perfectly horizontal when at rest, so there's a tiny difference between projecting vertically down from the ruler/tape measure to the actual pivot point and projecting at a 90 degree angle from the surface of the key.
But that's negligible.
Then the vertical (up/down) location of the pivot point (hardly) affects the relation of the pivot length (measured two dimensionally from above) and the ratio of the key dips at the tip of the key and at the fallboard. I can't put a number on it, but it's probably pretty small too. And the point was not to measure the difference in key dips at the front and back, but the pivot length and it has no effect on the "two dimensional pivot length from above".
Fatar is probably an extereme example of a low pivot point:
And Kawai the opposite:
And on acoustics and hybrids the pivot point is at the bottom of the key stick.
Here's a completely fictional and exaggerated example of the effect of the vertical pivot offset. The red arrows are the same length. (Of course different in vertical and horizontal)
There's no significant effect on anything. Looks like just a manufacturing oriented decision.