It does? I would expect the opposite, since codeine needs enzymatic activation in the liver. When you take it any other way than oral, it enters the main circulation first, and reaches the liver only after being "diluted" (means that it's been distributed among all the blood and some tissue as well); when you take it orally, it enters circulation only after passing through the liver - that means it enters the liver first, and enters it in "concentrated" form, so the enzymatic activation should be a whole lot more efficient. Only after that it (along with the now-formed morphine) enters the main circulation and is distributed among tissue (including the brain, but also the kidneys); and kidneys start excreting some of it. If it enters circulation before being passed through the liver, then metabolic activation to morphine should be less efficient, and also excretion should start earlier.
Well, that's what should logically happen. In practice, I've never really heard of anyone benefiting from other ROAs than oral. I'm a massive codeine-head, but I do CWE and oral is the only option for me, and it works well. If you don't mind, try oral with the same amount, and compare the results. I'd be interested to know if there's a difference, and whether it's significant or not. How much did you take, by the way?
Codeine is a very fast-acting drug, especially considering that it needs enzymatic activation. With oral ROA, I feel the effects as soon as 6-8 minutes after ingestion.