I fly a lot with TeeDee .049, Medallion .049 and Norvel .049s some stock and some modified. Each has various fuel likes and consumption
First answer for longer run is obviously more fuel and since I detest fiddling with very small hard tanks I use balloon or pressure bladders.
So in the Brodak Baby Clown not sure of your options for external tanks (I built mine for a tanked Black Widow) and I am curious how you did the engine mounting for TeeDee/Medallion but that is a side show ( I suspect the easiest way is the screw in radial mount back plate and I use this method on two of my 1/2a birds)
Buying and playing with all the small sized tanks gets tedious as most all of them need opened up to clean out the crap and verify (and fix) where the pipes actually ended up. That said I guess if you have the room just up the tank size to a full 1 oz. This is about the fuel load I put in a balloon or bladder to get around 5 minuets flight time after fiddling on the ground before launch
The TeeDee wants to be tuned and propped to be around 20,000, 21,000 Rpm to be happy and the Medallion some where from 15,000 to 17,000~ this is where they are at peak power and most efficient fuel wise. Stunt runs with the Baby Clown and either of these engines is going to be very fast paced as the Clown is better suited for the reed engine power to keep lap times reasonable. Even then my Black Widow Baby Clown only gets about a 2.5 to 3 min run off the 8 cc stunt tank
This all said I think the 6x3 and rich run is where you are loosing the efficiency of the Medallion and I assure you the TeeDee swapped in will drink more fuel for same setup and be a LOT faster doing it
A 1 Oz balloon tank is supper cheap, easy to use, and weighs less than the same sized tin tank
Most use of my Medallion and TeeDee are on combat planes so fast is what we tune for and I use propellers from 4.2" up to 5.5" and 2.5 to 4.5 pitch
If you are happy with the speed of lap time using the 6x3; keep that set up and just increase the fuel Qty to a full Oz. I have made side of fuselage tanks out of 35mm plastic film canisters. Most bigger cities have a old skool camera sales and repair store...they have plenty of these canisters usually free for the asking
Poke/drill small holes in the lid and heat with hair dryier then force 1/8th copper tubing for the pick up and vent. Run a bead of RTV in the snap on cap lip after test fitting a few time to orient the pick up to the center rear of outside. I even set these up uniflo and they work very good with the Medallion .49/.051s
Came back to edit this in:
What fuel are you using? For stunt use I recommend 25%N and 20~22% castor for the medallion, she will run fine on 30%~40%N but not needed for what you are doing.
I say this because I run 25% and 35% and the needle setting is dramatically different effecting run duration.
Another thought is your Medallion cylinder, is it true #2 with single bypass or has a TeeDee cylinder been swapped on with twin byPass?
Also, which head are you using, stock low compression of higher compression TeeDee trumpet head? I prefer Galbreath adapter and Nelson plugs and play with head shims to get good starting and long plug life with higher Nitro levels
Reason for these thoughts is the TeeDee was developed first to be an all out screamer but starting was a problem for the common sport hobbyist and they created the Medallion to be a lot tamer (but still more powerful than a reed .049).
These are just random thoughts and I understand you are looking for a good smooth stunt run as compared to my max performance reliable restart desires.
Basically what I am saying is there are a lot of combinations for each of these engines that can have a fair effect on efficiency and fuel consumption... Heads, (Merlin, Galbreath/Nelson, Cox std on High comp, GloBee) Head shims, cylinder shims (timing /compression), pressure or standard tank, piston fit, ball socket fit, crank fit/polish, heavy vs light propeller either in diameter/pitch or materiel, APC= heavy, vs top flight wood = light
Hundreds of combinations all have some degree of impact
I have .35 engines I never fiddled with, just break in and run, rarely changing fuel type or needle setting...Just about every Cox engine I use gets fiddled with a lot finding what I want, or just experimenting
Have fun brother the Baby Clown and good engine is a fun afternoon at the field