The coal goes right on top, you'll get a thin combustion layer just underneath the coal. It's not as difficult to control as foil over Shisha. A way to keep hot coals for several hours would be handy, maybe a metal can full of ashes. You might find the effect of smoking this to be interesting. I don't know if it's the near toxic levels of nicotine and/or carbon monoxide, maybe it's from just having to sit in one place for 3 -4 hours. It is very relaxing!
If you have some flue-cured leaf or maybe some up stalk Virginia, you could try it. Soak about 50g of it over night in plain water. Save a couple of good leaf halves for the outer wrap, the rest you can cut into strips about 3/8" (10mm) wide for the filler. I made the filler bundle up a little bigger than what I was going to attach it to, it makes it easier to attach. If you go back to the beginning of the thread, I pretty much had the assembly right. When you're done, pierce it length wise with a skewer until it draws well. For what to attach it to, this came to mind. Because of the taper, you may want to leave the outer wrap long to tie it off at the neck of the bowl.
I finally got some time to make an adapter to go between the Düz Lüle and my Hookah. It looks a little nekid without a handful of tobacco strapped on top, I think Sunday night I'll give it a test drive.
Well I have my new toys too. At the beginning of the thread I cobbled together a Düz Lüle, now I have a real one. The one I made is only 1 1/4" (32mm) diameter and the nicotine kicked my butt. This one is nearly 2" (50mm) diameter at the top! It has a male fitting at the bottom, so I'll need to make an adapter to go male to male. This may be an all day smoke.
So far, this is one of my favorite threads. So where did u get your duz lule? A tombeki on a 2 inch diameter holder would be overkill for me...i would think a smaller diameter duz lule (like your diy version) would have more day to day utility.