SLA Falloff

In order to better see how Falloff is being interpreted, let's up the contrast so that the midrange is compressed around the 50% zone.

Now it's a lot easier to see how Falloff is being interpreted.

Falloff looks at he orientation of of the normals. Where the normals are perpendicular to the designated direction (Y), it assigns a value of 50% (orange)

Here, I have redefined the Falloff axis as along the X direction

Now it is along an axis half way between the X and Y directions.

All of the above are demonstrated with World Space. Once you grasp how world space works, Object and Camera space will make a lot more sense as well.