What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

You don't say if you are using the same antenna on both ends, but the
environment is very different at each end. Consider that Transmitting is
about putting signal into an area, while receiving is about capturing the
signals in near field of the antenna, then discerning the intellegence. You
would have to analyze the output to be sure, but it may be localized
reflections, shading or noise at the street level. Because of this it is so
difficult to quantify range. There is equipment and software specifically
designed to do what you are trying to do but it is expensive. The result is
highly detailed signal strength graphic output overlaid on 3d mapping for
each fixed site at various frequencies. Most commercial antenna sites have
gone to great expense to generate those maps in order to show what their
tower does because it is very different for each location.