It is actually charcoal, not coal. While creating charcoal, logs/branches are loosing a lot of volume during the process. It is acceptable to make 1 unit of charcoal from 2 logs. Even 1 on 1 is acceptable. It actually forces us to increase log production when we get into metal works. I personally like 2 on 1 rate. But if you hate to create log automation i can understand you :) I myself hate to create cereal seed automation because of the low yield/messy straw production and the amount of bots you need to feed everyone in the map