I have a local Transmission daemon installed on default port and RPC path (/transmission/rpc/).
I have it configured with auth required.
If I only set up transmission-rpc-auth variable, I get an error message complaining about wrong RPC path. Setting up the RPC path variable makes everything work fine.
Not a big deal, just an annoyance, but I guess that transmission-rpc-path should keep its default value regardless of auth settings.