Poor radio reception and transmission IFD540

We are almost ready for the first flight of my Bearhawk Model B.  I've been doing some taxi testing as well as calling for radio checks.  Those that can hear me are relatively close.  Near the runway the ASOS antenna is about 2500' away and in my line of sight.  I cannot hear the ASOS unless I have the squelch on.  We did a high speed taxi test down the runway.  The plane behind me on the taxiway heard my call to take the runway.  However when I turned off at about 4,000' he could not hear me when I called to clear the runway.

I'm assuming this is in your Bearhawk.  where is the antenna mounted?  I think the fuselage is fabric covered isn't it?  Did you make provisions for a large enough ground plane?  I think you need a ground plane just over 2ft in diameter, on an all aluminum airframe this isn't an issue but on a fabric aircraft this has to be taken into consideration.