The amount that causes OD will be different in everyone. If someone uses 1 gram of heroin a day and they try to OD on codeine it would take them probably at least a few grams of codeine to do it, if they didn't hit the codeine ceiling first.
Short answer is, we don't know. I doubt you are reaching OD levels with doses like 225mg but only you will be able to tell what a dangerous dose is.
Codeine is weird though. The histamine release is really what is particularly troublesome with codeine ODs. Even with a massive tolerance to most opioids, life threatening histamine reaction can occur with as little as 400mg codeine in a lot of people.
Someone with a severe morphine dependency would probably be able to tolerate more codeine than a normal person in terms of the histamine issue, but regular old codeine can be quite the tricky drug (distinguishing it from DHC).
That said, I've known at least one BLer who took grams of codeine per day. Pretty scary from my perspective.
I almost died taking about 700mg when I had a dependency on 60mg or so of daily methadone.
I was so tolerant to the methadone I barely felt the effects of the codeine (normally 300mg of codeine and I'm happy), so silly me figured I'd be okay to push the dose of codeine past my safe limit of 300-400mg.
Not a good idea - I might have been tolerant to the effects of opioid agonists from the methadone, but I was not at all tolerant to the histamine release associated with opiates like codeine or morphine.
Long story short, after about 700mg of codeine consumed over about a 2-3hr period, the histamine reaction came out of nowhere in full force. It caused my neck to become so swollen I started choking, barely able to breath, and had to take a bunch of prednisone in the ER to avoid asphyxiating.
Pretty scary, although I definitely learned my lesson with it.