I am on my first build so please take that into consideration when reading my comments.
When I fired up mine for the first time I kind of cheated. I read that when the RMH is cold it can be hard to get a good draft.
I started a fire at the bottom of the heat riser to get things started.
I found that once the "heat riser" fire died, the feed tube fire was good and the heat riser was warmed up the draft was fine.
Obviously you can't do that in normal operations but it will at least show that your set up is good.