Everyone's situation is different, and there's no one guideline that would perfectly speak to all of them. So use your judgment about whether the discount tier is right for you. If you would struggle to afford the game at full price and need a little boost, opt in! It's on the honour system and you'll never be second-guessed about your choice.
"Below the poverty line" was the general yardstick that Avery settled on before launch, based on her local context and best faith effort. Because of the way Kickstarter's back-end works, the wording of rewards can't be edited after they've been selected.