Minus to PER rolls

[Rabbitball]

I know you're supposed to buy the relevant skills/powers when a character is permanently shrunk/grown, but what is the appropriate way to handle minuses to other people's PER rolls to notice you?

[Steve Long]

Bonuses to Concealment (Self Only) and Stealth. There are a bunch of examples in the Bestiary, Star Hero, and the like if you want to see some precise figures.