I use a 16 oz tank for my 160FX. That's more than enough to do a double round of IMAC practice, and helps keep the weight down. A 20 oz or 24 oz tank would work well for general or sport flying. I'm presently working off a stock of 10% nitro, but I'll probably try a gallon of my Moki blend and see how that goes (5% nitro, 14% lube). I use a regulator to enable tank on CG, but I see other installations fly well with tank behind firewall, standard fuel set-up. I had one set-up where the engine ran rich on a full tank, then leaned out as fuel level dropped; I fixed that with a Perry pump.

My sense of the rich mid-range complaint is that people are not willing to take the little extra time to tune the idle needle properly. It's called the idle needle, but really the two needles, low and high, work as a system, and both affect the mid-range. People seem to focus on the high needle for balancing power and reliability, and settle for less than optimal mid-range as long as the engine keeps running and pulls on the verticals. For sport flying, a rich mid-range is no disaster, but for a competition plane you like to hear a sweet note at every throttle setting. I tune my idle needle to the point where it dies or almost dies on quick throttle-up after 30 seconds of idling, then back off just enough that I can punch the throttle and get good response. When I get that setting, I then re-tune the high needle. Once the low needle is set, I leave it set. I don't think rich mid-range is a fault of the engine, I think it's a matter of tuning (which takes in fuel blend, glow plug & prop as well as needle settings... change any of these and you should re-check your tuning). Also keep in mind that as a ringed engine, it will keep getting better over several gallons. This is a honey of an engine.