The distance you are able to hear a mountain rescue unit from is going to vary very dramatically.
On VHF the topography (or if you prefer the terrain) between receiver & transmitter make a massive difference. If the path between you & them is clear sky, then the distance could be many tens of miles, even on FM. But if they are low & for example a few buildings are in the way, a few hundred yards is possibly too much.
Even driving up a slope towards a transmitter site can lead to a loss of signal. I know one location where a long gentle slope has a signal from a distant repeater across it all except for the last half a mile. And there, you are in the shadow of the top of the slope & on that last & highest section, you just loose contact as a result.