Why no FENCE_ALT_MIN for Copter?

Looking at Fences — Copter documentation it seems that FENCE_ALT_MIN only applies to planes.

Why isn’t this supported for Copter? It seems like it might be a useful thing to enable as a “training mode” so that if the student pilot loses control and the min altitude is breached the autopilot would immediately take over and RTL.

We had a PR that added this feature about 5 years ago.
But there was not much interest from users, so it never got merged.
But it should be easier to implement now that the fence code is shared between vehicles.

Interesting question. While you can set a Min fence in the parameters for Copter it doesn’t work in the Simulator. I was looking at a case of flying from a nearby mountain top with WP’s well below the starting altitude. Only Max triggered the fence.