2mg of buprenorphine, if you take it once and not taking it chronically (every day for substitution) is not high enough dose of buprenorphine to fill all of your receptors and thus block other opioids from binding. Given acutely, 2mg of buprenorphine will, in typical case, reduce some effects of other opioids (by the virtue of binding and not letting go off receptors that it has filled) but after, let's say, 12 hours, even buprenorphine will be somewhat metabolised and cleared off from the receptors. Bigger the habit (opioid tolerance) lesser the effects of 2mg buprenirphine and more receptors for other opioids to work on (if I understand the mechanism correctly).
I have made a mess off it and will summarise now. If you have moderate/high tolerance to opioids and you have taken 2mg of buprenorphine only once in last week or so, my opinion is that you will feel most of full agonist effects later in the day. Longer you wait, obviously, less you will waste. But if you're taking heroin, high dose of oxycodone/morphone, hydromorphone or similar high potency opioid - you will probably feel most off their effects. If you are taking fentanyl you will feel it almost normally as fentanyl is one of few opioids that can actually compete with buprenorphine for the receptors and win the fight. So, it all depends on much things, but this is what I can tell you given the data in your question.
The other thing, regarding precipitated withdrawal -> if you take full agonist after taking buprenorphine and not take any buprenorphine after that you will not precipitate withdrawal. Withdrawal is precipitated by buprenorphine kicking out (outcompeting) other agonist that are exerting stronger effects on opioid receptors and thus reducing general opioid activity. When taking full agonists after buprenorphine only 2 things can happen - either full agonist has no effects or opioid effects are intensified. But be careful if taking buprenorphine after taking full agonist because that is where the danger of precipitated withdrawal lies.
I hope I have helped. Although above response basically said the same thing as me, I wanted to elaborate a bit.
Take care.
