Are you doing full sheets? You may have to create a frame to support the material because the gas pressure will vibrate the sheet. You may want to shut off material sensing in order to cut it. You may also wish to consider coating the material with Malox and let it dry for about 5 minutes. The Malox will help minimize back reflection during the pierce. use Nitrogen as an assist gas (3-6 bar)and a starting feed rate of 8,000 to 10,000 mm per minute (you can always go faster if you can).
-HR