Welcome, as an Internist I will try to answer your Medical Question, for informational purposes only, please see your doctor as needed.
you are in a sense correct in your assessment
methadone, like all opiates, binds to opiate receptors, there are 3 types, kappa, lambda, and delta
and it is a "neutral" agonist, meaning it binds receptors, and has good pain control, but there is not as much euphoric sense.
Dilaudid is more of an opiate agonist, it exerts more pain control (and euphoric sense) than methadone. so from a relative comparison, methadone is blocking sites from the effect of dilaudid.
there is another neutral opiate agonist, buprenophine, that you can consider when using methadone for better pain control.
please get back to me if you have questions I can answer. Dr Frank T