Should Caffeine be avoided while on MMT?

[baron samedi]

Just wondering what peoples thoughts are on this. SWIM is on 45ml methadone and is also a big fan of drinking tea (of all varieties), but not coffee. He would love to be able to drink at least 2 cups of tea daily, but his instinct on the matter is that even a cup of tea might have an adverse effect on his methadone dose.
He imagines that the vast majority of people on MMT drink caffeinated drinks without thinking twice, but being a worrier and slightly obsessive SWIM has recently cut tea out of his daily routine entirely. He did sometimes feel after he'd drunk a cup of tea that his methadone just wasn't working right.
Is SWIM really being obsessive about this? Surely a couple of cups of tea per day cannot really have that much effect on the metabolism of his methadone. In another thread however, one poster with significant knowledge of methadone pharmacology seemed to concur with SWIM that even low doses of caffeine can interfere with methadone.
What is the general consensus?