This is from a reply I got from Kelsey about his restrictor plates.
Yes, 3/8" above the joysticks. This is a common mounting depth for the Happ sticks. The locating pins require 3/16" deep holes and the removable pins require 3/8" deep holes. I've attached a cross section of how the restrictors are typically installed.
Clarification on that: When I revised the mounting plate connection with the headless bolts, I also improved the locating pins. I totally forgot about that until I saw my own words repeated.

Instead of the previous straight pin that extended 3/16" below the restrictor, I now use a grooved taper pin that extends 3/8" below the restrictor. I would have liked to keep the pins only 3/16" long, but I had to use the shortest available grooved taper pin I could find anywhere. These new pins grip a little better than the previous straight pin and help reduce any "slop" that may be present when not using a screwed connection on the mounting plates.
A closeup of the new pins
can be seen here.
Thanks for bringing that to my attention, SP.