On-table Artillery in Contemptible Little Armies

[Strelnikov]

After some games with Contemptible Little Armies, we have a doubt regarding on-table artillery fire. There is a procedure in page 11 (Artillery On-Table Battery Fire) and what seems a different one in page 20 (Field Artillery). Are both applied simultaneously or is it the one of page 11 intended for on-table indirect fire and the one of page 20 for direct fire?

Any help will be much appreciated. We have our next game scheduled for next saturday and my Politruks are becoming increasingly nervous with my por artillerymen.