Dangit, I woke up for this?
Seriously, you really want to experiment with this, because you will learn all sorts of subtle details. I have to admit, I used to get alcohol spills in the old days, and that was one of my primary reasons for shifting over to Esbit, but that is just me.
Right now in my equipment storage room, I have three different packages of Esbit fuel, each with a different brand name, and I see different performance, different residue, different blow-out and re-light action, and probably some other things. So far this summer, I have gone through at least three or four boxes of the stuff.
The colder your cook pot is and the colder the water is in it, the more sooty residue you get on the pot. Actually, what I get is a brown/black sticky tar. Once you finish one cooking session, if you immediately drop that sticky pot into a storage bag, now you have sticky crap all over the bag. So, I let the pot cool completely and the residue hardens somewhat. I transport it in a disposable plastic produce bag, so the residue doesn't get all over everything. There must be some things that can be done to adjust the flame space to minimize the residue, or maybe I am keeping the bottom air venting choked.
If you put a soap layer on the pot really good in advance, the soap layer will protect the metal surface from residue, up until the point where you accidentally wipe the soap layer off. Been there. Done that. I'll bet that there is some perfect kind of soap layer that you can use. Must experiment.
I find it best to use a full cube in the fuel tray. Then I boil a cup of water, then I blow the fire out, and there is at least a half cube remaining. Also, that used cube (depending on brand) has little spiky Esbit crystals sticking out from the surface for a tenth of an inch. Maybe 15 minutes later, I relight it easily at the crystal surface and do another boil. Once the meal is finished, if I have a partial cube left, I drop it back into the Esbit packaging (foil and plastic) and carry it to the next camp. When I blow the fire out, I do not want to breathe the smoke or fumes, so I do it quickly.
An alternative method is to take a full cube and cut it in half with a knife. Unfortunately, some brands tend to shatter, so you are pinching up little white flakes from all over. There, you would really need a fuel tray.
If I am cooking something big, I use two Esbit cubes together, placed vertically on the fuel tray. I don't think that is more efficient, but it is quicker. However, most of the time when I backpack with a friend, we use a tiny butane rig instead. To me, Esbit makes best sense in mild conditions and for solo water boiling. Just don't make me go back to Louisiana!