Pekka
There could well be an ideal taper, unknown to me. The length of the taper is the thickness of the head. The angle will depend on how big a piece of wood you have for the handle.

As the handle has to pass through the finished taper, this does restrict the options.
If I was making one anew, I would finish the angled striking faces last of all,
after fitting the handle.
If you need any exact details, I can measure it for you.
Pete