As Riese gains more Tsun-ergy, the potential Dere grows in response. Sooner or later, she'll fall out of whack and be mostly Dere.
Edit: Also, to be fair, the manga has lowered the amount of perversion Zeolith actually has done in comparison to the WN. I can't say anything about the LN. Don't ask for direct examples because things aren't in line, and I'm not sure if during my skimming certain events won't still happen.