The way I understand it, the ArtNet universe ID is assigned to be the OLA universe ID modulus 16, but the ArtNet net and subnet addresses depend on the config file and not the OLA universe.
This makes it more complicated than necessary to assign an ArtNet address if your universe ID is higher than 16. For example if you have universe 17, you'd almost certainly want the ArtNet address to be 1.1, right? But without messing around with the config file or the ola_artnet CLI app, you get 0.1 instead, same as if you had used universe 1.
My suggestion is to have an optional flag in the ArtNet plugin config that, when enabled, automatically sets the net and subnet based on the OLA universe ID, the subnet being the OLA universe ID integer-divided by 16.