Thanks for the tip. It worked. No more distortion.
I don't want to make it drop slower till 15khz because arround 7.5khz and 9khz there are very bad spots which seems to be the main cause of sibilance and harshness(detected both on sinegen). There was also another one arround 11khz, which I now dropped too. Looks like I eliminated all traces of sibilance. Now I need to decide which signature I like better (with or without EQ).