Rig slots mods and the law of personal gain

So still kind of new to Eve Online and notices some of the slots have high negative attributes. This got me thinking and figured that there should be a rule of gain for such slots. Basically the way this works is if a Rig has say 10% bonus the negative attributes can only be 50% or 70$ less than that so say you get a bonus for an item say 100 the negative side of things would be -50 or -70. Generally the negative affects from a Rig should be much better than an similar item in a mid slot.