I think I may have stumbled onto something when I built my 57 Nobler. I built it as per the kit even so far as the tank design and I put a Fox 35 in it with a 10x6 prop. It flew great, except that I discovered it only lasted about 5.5 mins which wasnt enough time to fly the full F2B pattern. After checking around I learned that the tank design was only 3 oz.
So rather than re-designing the model to fit a larger tank, I simply soldered a 1 oz hopper on to the bottom of the tank on the inboard side and made a few holes (like a baffle) between the two compartments.
To my surprise, this worked exactly as I had intended it to and what's more, now if I ever get worried about an overrun, I simply pull up and fly high and it cuts out within one lap. As such I have never had an under or overrun flying this model.