re: Fence post

I built a friendly neighbor fence about 20 years ago about 150’ long.
While doing my homework I read that instead of going with a bigger post every so often go twice as deep every 6th the post.
The fence is 6’ high. Post were spaced 6’ apart. I started with a 10’ post cemented 4’ deep, then 5ea 8’ post at 2’ deep.
Repeated this process for the length of the fence and put the other end post 4’ deep.
2x4 runners with dog eared pine fence boards.
Has held up through the years, only replacing a board or two every few years.