Its pretty hilly between Mullumbimby and the Murwillumbah and they’re about 30 km apart.
Finding a suitable spot for an FM signal to cover both Murwillumbah and Tweed Heads could be a challenge (Springbrook doesn’t get into Tweed Heads very well). Might need two separate sites.
And 104.1 sends most of its signal north at the moment from Elanora (so I think most Tweed listeners would still be on AM) but once an FM conversion happens, increasing the power to the south would cover Tweed (but not Murwillumbah).