Yes, that is ticked. The figures are quite considerably off so I don't thing it's anything to do with commission.
Aha - I was just about to take a screenshot when I figured what it is - If I'm laying and want accurate "what if" figures I need to ensure there's a zero in the Backing amount box (and reverse for backing).
Sorry to trouble you, it seems to be working correctly as long as I remember to put the zero in the opposite box.