Hi Artw.
I also have an AV8R with a PST J 600 engine, and have a 50 oz Dubro main tank and BVM UAT.
I fly for 6 minutes and always have about 8-10 oz of fuel in the main.
Also almost never fly the entire flt at full throttle.
Am using 70 oz in my new plane for my PST J600R.
Ron