FM stations being received 100-200 KMs away from the originating city is no miracle, just pure electronics. How far the signal will be received depends on:
(1) The power of the transmitter - An FM transmitter is just an electronic device that broadcasts electronic energy. Don't faint, but what it broadcasts is actually electric current. Why we don't get a shock by it as we do with normal electric current in our household, is because the power transmitted by FM stations is so less in comparison. An FM transmitter that broadcasts 10 Watts of current (in form of modulated wave energy), can be heard 100 miles away (aerial distance) or even more. See this:
All about FM and AM radio broadcasting: PCS Electronics specially the picture at
http://www.pcs-electronics.com/schematics/max1rack2.jpg
(2) Availability of LoS (Line of Sight) - FM Signals travel in straight lines. For best possible reception an LoS is required. A person nearer to the transmitting station may not get as good a reception as person much farther but having a better LoS.
(3) Capability of the receiver - The reception also depends on the capability of the receiver. A good receiver can catch and demodulate signals that an ordinary receiver will simply ignore or won't be able to process.
(4) Electric interference - We don't realize it, but there is so much of electrical interference present in our environment. FM reception, like any other device working on RF waves, is subject to electrical interferences. Take a mobile phone with FM near to a computer's CPU when you are listening to FM, the sound quality will drop considerably, take it away, the signal improves.
In brief, it is absolutely no miracle that Mumbai FM stations can be heard in Pune. I'd say, if you use a good external antenna, you can hear Mumbai FM stations in interiors of Maharashtra.
~ Ranjeet Rain