General rule of thumb and your results will vary depending on strong in-band signals, transmitter power/antenna and your antenna, but the "trigger" range is typically...
50' for portables
100' for mobiles
1000' for repeaters/base stations
It's called "Close Call" for a reason.
And yes, when I'm out in the country I can get CC hits on VHF repeaters at 400' from several miles away, but this is not the norm.