What are the different forms of opioids and their potency

I’ve heard terms like ‘desomorphine is 10 times more potent than morphine’. I’ve heard heroin is twice as potent as morphine, however I don’t know if that is because it passes through the blood brain barrier easier or if it is better at activating receptors.

So how does the potency list work, what are the most potent form(s) and what makes them so potent? Are they longer lasting, have a stronger affinity for the receptor, cause more activation, or what?