Just make sure that you don't have sharp corners on the haft, as they are weak points. If you need to make the haft smaller to fit the eye, then file & sand it down to fit so that it's all smooth curves, without shoulders.
When my first felling axe split, it was because the (chinese) factory had sawn a shoulder at the eye. It looked from the outside like it was properly done, but that's where it split, sure enough.
Dad bought a new hickory haft & showed me how to do it properly with the replacement, and it's still going strong 15-odd years later.