Resist rates seem too low

[Domingodarkrage]

My players have noticed that they are able to consistently land spells on mobs much higher in level than the player, 10-15 levels higher. The casters love this, but I'd like to make it much more like a live server, where a level 31 necro could not solo a sand giant and earn insane experience.

I've looked for threads, and found not real leads. I've modified some values in rules_values and resulted with no change in resist rate. Specifically, I've changed
spells:AutoResistDiff from an original value of 15, down to 8, and further to 4. No change in resist rate (level 35 able to land spells on a 50)
Spells:ResistperlevelDiff from an original value of 85, to 120. Still nothing noticeable.

I saw a post mentioning the method to determine a resist has changed to a more live-like method, and these rules are no longer used. Does anyone have a suggestion about how I can go about changing the resist rate to make my server more fair?

Thanks for any suggestions.