When adjusting the priority, the combinator just uses the Depot Priority instead of verifying the type of station. IE adjusting priority on a station selected as a provider, it will set a Depot Priority instead of Provider Priority.

There are 3 possible priorities to set. Provide priority, Request priority, and Depot priority. Making any changes to these values in the combinator results in the correct signal to be emitted onto the wire. This can be verified by inspecting a connected power pole and see the signals on the attached wire.

From there it is up to LTN to read those signals and adjust its behavior. For those priorities to have an affect a wire must be connected from the combinator to the station input lamp.

My apologies I didn't see the priority on the right. I was thinking that the priority on the left was universal and selected based on station type. Note to self playing tired is not a good idea XD.