Glad you liked it!

Haha, cannot explain anything like that in a comment here. It is too broad a question. But basically, the two sequences are used for different things. Post-heaven is used for doing stuff in the real world, for example setting up a grave or house (fengshui). Pre-heaven is often used for talismans or things that are timeless. Of course, there are exceptions. The trigrams are like a deck of cards. Just like different card games have different rules, so do different uses of the trigrams. Sometimes pre-and post-heaven are superimposed on each other, but mostly each has ways it is used. and not both at the same time. In medicine, we would tend to favor post-heaven as disease happens within time and space.

Thank you that was a wonderful explanation. Its almost like the pre-heaven describes another dimension with slightly differ laws. Sometimes I wonder if referring to the pre-heaven sequence might be useful related to the Qi Jing Ba mai.

There are two methods that use time to select the opening points of the 8EV. These 8 points are associated with the 8 trigrams, but those two ancient methods use the post heaven order. I think seeing the 8EV as pre-heaven is more influenced by some modern teachers in the west, like Jeffrey Yuan. While of course chong and ren have some pre-heaven aspects, not all 8 do, if you read between the lines in the old books. For example, what do the qiao and wei vessels have to do with pre-heaven? Nothing in the old books.