It was the same diameter right next to the MAF, but it did remove other restrictions like in the fender, and it was a smoother path between the filter and the throttle body.
Here is a good example of what I am saying about the CAI's I have dealt with. both were exactly this same idea.
the only think that I can think of that would affect airflow is that the air maybe be relatively faster or slower in that part of the tube versus what the stock tube would read. since this can affect that area without the MAF reading it (because like someone said the MAF covers only about 14% of the circle of air in question), that is why any adjustments would need to be made.
