How to set metatags on entity edit forms?

Metatag doesn't effect the meta tags on entity forms, you should look at core's APIs for that. Sorry.

Ahh.. good to know. Thanks for the reply.

Would it be unreasonable to think of that as an added feature? I.e. "add tag definition by path" either through ui or a hook. Would think a shame to lose all the advanced tag definition provided by this module to go with a simple core hook to modify these in code.

Did you try the included metatag_route module?