kleo,
It is very hard to get a fixed end connection with timber piles, here you have to assume pin type connection, or have a nice deep pile cap. For concrete piles that are assumed to be pinned at the top, you generally only supply 50mm embedment. Some people provide enough reinforcement to ensure ductility, thus that the connection can go into plastic deformations but be assumed as pinned. Some don’t.
When in doubt, just take the next small step.