Here's some interesting info about getting the most coverage in low power to BETS-1 and part15 FM transmitters
http://www.engineeringradio.us/blog/2011/08/fm-stereo-vs-station-coverage/
This is why Decade MS-100 comes in mono and stereo versions, and why it's selectable on the stereo one. Ramsey's and the wholehouse 3 also are selectable.
Mark