What you might want and/or need is a true chicken hopper set up, where you have a large inboard tank that feed a smaller tank mounted outboard. The best examples of that I ever saw was on carrier models. Most of the bigger profiles had heavy ball bearing engines, so to get them to balance and hang on the lines correctly, you want a short nose moment. Bill Calkins designed the profile Guardian that Brodak put out and there may be info on those plans. The late Jim Thomerson had a great explanation with diagrams and such on Stuka Stunt that would be very helpful but that isn't around any longer. There are some tanks out there in production that have a small tank attached to the edge of a larger tank, but those are actually just a baffle type tank. While they make work well, they are not really a chicken hopper. I have had problems with those from having the pick up so far outboard, where the engine wants to lean out after it gets airborne and some centrifugal force starts to work against the fuel flow. You can also just fabricate a custom uniflow tank yourself by making a wood block form and dummy to the dimensions you need, then form the sheet tin stock around it and put the tubes where you think you need them. It's part of the hobby and a good skill to learn.
Type at you later,
Dan McEntee