Whether or not you make a true wood gas stove, putting in a raised floor, helps let the ashes drop out and air get in.
This is the single BEST modifcation to a normal hobo stove (IMO). Also, it helps in lighting as you can put tinder underneath the 'floor' and let it burn freely.
Note: the floor can be wirecloth like the one risk shows. It can be the 'top' of the tincan with a bunch of holes punched in it... also, insteat of cutting 'flaps' and bending them up like risk does, you can poke holes and make the floor self-supporing (corners of wirecloth bent down). All the methods work.
eidt: all of the commerical hobo-stove (trailstove, firespout, etc) as well as the nimblewill stove (see pattern on thru-hiker.com or zenstoves) utlizie raised floors.