Elemental resistances will reduce element-based chaining rates. An enemy who absorbs or is immune to an element will only get 25% of the chain amount. An enemy who is resistant or halves an element will only get 50% of the chain. An enemy that is normal or weak to the element gets 100% the full chain amount. You also get a small bonus (+0.1%) if you are attacking a weakness, which grows to a more substantial bonus (+0.7%) if you are varying your attacks.