Defense bonus at Epic Levels

Bearing in mind that I have never played epic games, I’d suggest epic defense bonus rise at a rate of +1 every 2 levels, just like epic attack bonus.

Feat Masteries at Epic Levels

You’d also need to do something with feat masteries for characters over 20th level: how fast their masteries improve, potential for feat masteries of 11 or more, that sort of thing.