I can't seem to get this part of RMH

I can't seem to understand the building part ,the one that connects the down part of the heat exchange barrel
with the flue that goes though the mass.
Ianto Evan's book writes about this part?

''In order for gases to flow smoothly through the tight gap between barrel and flue as they
enter the thermal mass, there needs to be extra space all around the bottom of the
barrel, a ring-shaped channel that collects the falling hot gas and directs it to the flue. As
this is a prime trap for lightweight ash, make it big enough that you could get your hand
or a vacuum cleaner tube into most of it. This channel needs to extend all around the
base of the barrel, dropping and widening from above the bridge to the clean-out/ash
pit where the flue begins. Shape it in a sandclay mixture without straw, leaving the sides
and base really smooth, so that a clean-out tool can rake out ash without snagging''

I am lost at this.I can;t even get the picture of what i should do. Do i leave an empty space down the exchange barrel
and then build a half-ring frontier where on its center there is a flue opening?
Thanks for any help

Check for the post "flue transition / plenum pictures", it will have pictures showing this area.  This must be the largest section of your exhaust.

I read up as much as I could and then just winged it.

Here is my complete build :

https://permies.com/t/40107/hot-barrel

The clean out should be a nice large space, for the ash too settle into, before going into the pipe - in the mass.
With enough of a drop to hold a fair bit of ash.

I kept in mind - that in one of the videos I watched,  it said "when you are designing your ash trap, build what you think you need, then make it bigger "  - - - so that is what I did.  

Hope this helps.

Have a look at my pics.

That is really helpful.Thanks.
So you just leave this big space and you don't use any additional pipes to direct the heat stream from the barrel to the T section right?
Just an open space?
I don;t think that there is a actually a video that shows you step by step the whole process.That  would be really helpful.

Yes, an open space, think of it as a mini bell. Form an ash pit that is the lowest point. Your horizontal pipes start there.

I was going thru the old pictures of my RMH build, and found these pictures of when I raised the barrel up . . . shows you the "channel" for the hot air to be funneled into the ash pit . .. .