Monster gain exp gap

You can gain exp from a monster that is 5 levels below your level. And you can get exp from monsters ~ levels above.

I would like to change this so you can only get exp from monsters the same level as you. If you kill a monster below or above your level, you would gain 0% exp.

I searched the source and found "void CUser::ExpUpSetting". But changes to "if( GetLevel() > 5 )" won't work.

Can someone give me a hint?