Naw, avoiding percentages (20% is way too much) like that is why I'm trying to stay away from traditional currency in the first place. Besides, my book isn't for sale anymore. I want people to pay me after they read it, the more I think about it the more that's the only really fair way to do it.
The way I see it I'm privileged to have a reader, they aren't privileged to be reading my work no matter how hard it was or how long it took me.