What Richard (Craggy Aero) said, and:

The placement of a transmit or transceiver antenna will almost always be more critical than a receive only antenna. This is due to obstructions or interference causing nulls (areas where the transmitted signal is suppressed or blocked) and impedance mismatch causing high SWR, i.e. power to be reflected back down the transmission line (coax) and wasted instead of being transmitted by the antenna. Thus antenna installation for the PF A antenna is extremely important as it has a minuscule output power of only a few milliwatts (I read 10 mw somewhere, but can't find it now).

On the other hand, you could probably hold up a paper clip and receive the ADS-B signal from even a small power aircraft that has a minimum power output of 75 watts, larger aircraft 125 watts minimum, up to 500 watts max. Optimal ADS-B installation in your glider, while important, would hardly be an issue.