Ok "affinity" it's how strongly it would bind to a receptor. Then there is agonism or antagonism which can be partial or full. Full agonism is the "strongest"

Ok "affinity" it's how strongly it would bind to a receptor. Then there is agonism or antagonism which can be partial or full. Full agonism is the "strongest" activation that doesn't have anything to do with affinity because it just means it fully activates the receptor, the affinity is how likely it will be bound to the receptors. For opioids that are full agonists potency and affinity can be used essentially interchangeably these are all primary pain relief opioids and fully bind to the receptors in the same manner essentially, opioids which are mixed agonists or even antagonists such as those used to treat addiction or withdrawal can have very high affinity but low potency because while they bind to the receptor very strongly they don't fully activate it or even deactivate it but as their affinity is high they can beat other opioids to the binding and block the receptors. As this drug is a replacement for fentanyl it's a full agonist opioid which means that if it's more potent it has to have a lower Ki value which means higher affinity at a matching ratio.