EXP experience gain

Hello, I am now lvl 65, on nightmare difficulty, just started 10-1 stage. 

I got 3 stars, and total exp of 1000. Why is this? 

 

when i was a few levels lower, on stage 9-1 and 9-2 I got 3000+ exp for 3 stars. how should we level up while receiving lest than 1000 exp per level, which is 1-2% of our level? 

Nightmare 10-10 cleared 3 stars, 3724 exp, what is going on?

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[IMG]http://i68.tinypic.com/214vcli.png[/IMG]