How does exp penalty work at high level?

So according to http://pathofexile.gamepedia.com/Experience my safe range for lvl 90 should be +-8. So 82 maps should yield me 100% hp.

But when I enter my stats on http://poetools.com/experience-penalty/ I get 50% xp rate on lvl 77-82 maps. And whenever I add a lvl all the maps from 77-82 gets reduced by the same ammount.

So how does this work really?

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Shagsbeard wrote:

http://pathofexile.gamepedia.com/Experience

Did you even read my post?

You level up slower because you're getting reduced experience. That's how the exp penalty works at high level.

GGG doesn't intend for the average player to reach level cap, it's better if you reroll around level 90.