SK,

I have the same tank as the one shown in the pictures in the posts above and I don't think it could be made any bigger and still fit into the airframe. It is semi-oval shaped to match the former cut outs in the main body and extends from the back of the tray bulkhead to just in front of the turbine. The only way I could see to add more capacity would be to add a tapered bulge at the back of the tank. You might gain 1/2 a litre.

There is so much room in this jet under the cockpit cover you could put another tank there. I did this on my Reaction to add a 32oz smoke tank and it worked well. Only issue was all of the smoke fluid was ahead of the CG. [&:]

PaulD