It's possible that the remaining 4% failure rate in the Glock is due to the Glock 30's ejection pattern. The round being extracted in a G-30 hits the top round in the mag pretty solidly. If the rounds aren't crimped, the round being ejected catches on the case mouth of the next cartridge at the top of the mag, knocking it off the extractor. That's why SWC's (plated and jacketed) don't work well either. You can expect about a 40% failure rate with SWC's.
It still might be a velocity issue too. Can you use aftermarket springs in IDPA?