I suspect that in practice, suppressing transponders at the exact same altitude will have no much affect on PCAS reliability, as relative altitude between aircrafts fluctuate all the time, especially with gliders, and I suspect the suppression algorithm can detect altitude fluctuation and does not suppress it. This is just my guess based on the fact that my PF seem to do good job with PCAS alert even when flying at the same altitude as someone else.

Ramy