I saw that thread, but in that thread, my question is not explained.
It is; it's in the first quote, under the bold "The way activity is calculated" text.
So its best to make 14 posts in a week two weeks?
What is i make more, i get punished by not getting full or senior?
If your only goal is to rank up in the forum and doing the very least of what you can do, sure. 14 posts every two weeks will boost your activity the maximum it can become.
It's not a punishment whatsoever. It's just that ranks here are based on how long you've been here, not how many posts; otherwise people would just do some LQ posts and become a high rank instead of actually having to be dedicated to the forum to achieve a rank like that.