So would a decent formula for drugs A and B be: rAdiff x rBdiff x rshared = r% where the rA/Bdiff is the chance of resisting the unique parts of A and B and rshared is the chance of resisting what is shared between them?
Right. I'm definitely oversimplifying.
I'd say you were just simplifying, no over- about it. That seemed like a good level of simplicity for the explanation.