You’ve identified an important point, which concerns how COM is used.
If one usually scans RM for a provider and identifies a possible hire, then goes to COM to check feedback on him, there’s no need to have location in the COM subject line.
But if one usually scans COM for a provider and identifies a possible hire, then goes to RM to check details, then having location in the COM subject line has been hugely helpful (while making no difference to a RM scanner).