Let’s say I have a maximum resist of 80%, but I have equipment on that could give me up to 100%. If I get my resistance lowered by 20%, do I now have 60% resist, or does the excess resist keep me at the max threshold of 80%? Thanks to anyone that knows how this works. 
You would have 80% after the reduction. It is not wasted.
I beat fhe avatar with 190% lightning resistance, so its not wasted against res reduction