FX Reduce plenum size on FX Panthera

I had a question about the Panther. Right now I’m getting closer to getting this rifle tuned but noticed even with dual bottles at best it gets 3 mags. My Impact Mk2 with 58cc plenum with 580cc bottle at 300 bar gets 3+ mags. Is there a way to reduce the amount of plenum size safely to reduce the amount of air to make it more efficient. I don’t shoot anything over 31g slugs and typically like the speed from 970-1000 for long shot pest control.