I going to "guess" a bit:

I understand the FCC restricted the transmitted power output of the
PowerFlarm over what PF would have liked. They also refused approval
unless PF took steps to prevent someone from installing a high gain
antenna in order to improve output power. This resulted in sub-optimal
transmitted range, though I thought it was still supposed to be 2 to 4
miles or so. PF did include a "panel" Flarm receive antenna that is
"optional" to install. Using that antenna will increase the effective
range of the PF by displaying threat aircraft at a more distant range.
If the threat aircraft doesn't also use the "panel" antenna, then
you'll probably see him before he sees you.

Were these additional receive antennas used at the contests or left in
the box?

In my flight testing with PF in two power aircraft, effective range
was about .5 to 2 nm, without using the panel antenna, and seemed
dependant on aircraft orientation as one would expect as sometime
there was aircraft structure in the way. I'm using the panel antenna
in my glider, but so far have not found anothe PF equipped glider to
play with.

The "ADS-B in" works flawlessly all the way out to 32 nm. The PCAS
function seems reliable to at least 8 nm, however the altitude
displayed will sometimes show a minus instead of a plus when clearly
the threat aircraft is above.

bumper