For a percussive sound, you will want a short attack time, fairly long decay time, sustain level low (zero), and long release time (similar to what decay is set to).
The decay time is just as important as release here, since if the decay has already been passed, there is nothing to release (sustain level is already zero). There is an interesting quirk with this because with short decay/long release if you hold the note it "blips" but if you hit it quickly it will ring (since the release takes over at the note off signal which should still have a sustain level component).
Edit: The blip/ring phenomenon noted above is a common thing to synths. By setting the decay time and release time to the same values, they both have similar "curves" so when the note off is received the release picks up where the decay left off (with the same rate), but gives you leeway in when that note off message is received. In your situation, I would suggest mirroring the decay and release times to taste.