Same as they would their mobiles, hopefully. However, and this is one of the downsides to a system, and a system that does not have a good repeater/repeaters setup, in-building BDA's if needed, are at a loss BIG time with portables. Ringwood PD is a grand example of this. Their mobiles are putting out 45-50 watts and have no problem reaching their repeaters. Their portables, another story, even outside, forget being in-building or down in a ditch/low area on a call. Even if with 5-6 watt VHF portables, it is usually not good...
Good systems take time, development, and a lot of money to develop correctly.