4/4 is a good baseline, don't try to fine tune the feed/air until the boiler is really running 24/7 for a few days heating your house. What will happen is once the stoker shuts down for the off cycle you'll see the black spot in the center. If you increase the feed or reduce the air the black spot will get bigger, decrease the feed or increase the air and the spot will get smaller. Check some previous posts on the ash ring, I'm not an expert but I think about 2" is good. The goal is to have a cool feed pipe and very, very little unburnt coal in the ash bucket. As far as the uneven fire goes, I'm thinking that the air holes might be plugged up on the right front or there is a hole in the grate on the left rear, or maybe the air pipe isn't all the way in?