Ludwig Acrolite P83 strainer

[Blue Note]

On Acrolites the P83 is mounted using a flat washer between the strainer base's two "feet" and the outside of the shell. So the P83 stands off from the shell with only the washers touching it. On the butt side there are no washers used between the mounting feet and the outside of the shell.
Why are these washers used on the shell's outside and only with the strainer and not the butt?

On Supra-Phonics, there are no washers used on the outside between strainer and shell.
Strange Acrolites do have them.

[vadrums]

I've had wrapped wood shells with those small washers on both Ludwig & Slingy's. They were used to space the strainer and/or buttplate away from shell/hoops. Strange to have those on the metal shelled snares though...