Profession: Item Creation v. Recrafting


So I can craft a new item at level 5, but when I want to improve the existing one I only reach level 4? How does that makes sense?

Math supports my theory:

* New is 480 or 495 with optional item, skill is 386, so delta is 94 or 109 * Improve is 495, but skill is only 343, so the delta is 152 * So the diff of the delta (w/o optional) is 58 which is exactly required to reach the border to level 5

But how come? Any particular specialization I need to invest or did I simply create more new items than improving some, so my skill in creation is "by experience" higher than in improving? If that's true, I'd rather build the item anew and never improve, b/c that's cheaper in the long run, isn't it?

Thanks for any guidance.