Any play you think is bad should go in subtractable losses IMO. Not necessarily getting it in behind, just playing bad. So if peeling a 4bet is bad, that goes as an avoidable loss. If you then flop bottom set and play it perfectly, any money on flop/turn/river aren't avoidable losses - they're just normal plays. Never subtract anything from it and let it keep growing.

Expected losses would be most accurate but I like avoidable losses as a 100% figure - it's the worst case scenario, it's easier to calculate and a bigger number will inspire you not to do it more.