[quote=@Lugia]
I think what he's looking for is more or less -5, rather than -X% damage. Dunno why, but he seems to like +-constant values. What you could also do is make it so he has -2 STR while this is active, so it's not a completely positive increase to your stats. I dunno, though, I mean, I'm not the GM so I dunno what he'd like to see.
[/quote]

The flat rates are for simplicity's sake. It'll help with the calculations and make things flow smoother. I'm not opposed to percentages, but there are some people who might be intimidated; and avoid putting them on their sheet.