[KLS]

You can change it to be more severe if you want to delve into the code.

Around line 4040 in spells.cpp you'll find

	int level_mod = temp_level_diff * temp_level_diff / 2;
	if(temp_level_diff < 0)
	{
		level_mod = -level_mod;
	}

	if(IsNPC() && (caster->GetLevel() - GetLevel()) < -20)
	{
		level_mod = 1000;
	};

Which deals with the level mod. You can also change the -20 to make it a faster cutoff.