I'm under the impression I win what I stake less commission, plus get back my liability. So if a horse loses, I'm ahead as I win my stake and it will b more than 0 regardless of commission. For arguments sake, I stake 6 with a liability of 100 so 106 is removed from my account. I win my lay and get paid 106~ (my 100 back plus 6 from the backer less commission).

Or am I missing something?