Please check our conclusion about 'a preposition before prepositional phrase'

We questioned whether a preposition before another preposition is gramatically correct or not two days ago here.
After that, We've got a lot of answers of how to analysing that structure in many ways. :-)
Now we will post our conclusion about that, and of course we want another feedback from you.
Please help us one more time. ;-)
We concluded our research about the English grammar

concerning preposition after a preposition.
1. prepositions don't necessarily have to govern noun phrases only.

Some prepositions can also govern a prepositional phrase.

Such prepositions are "from" and "until".
ex) He came to and knocked the burning cigarette end from between his fingers.
ex) This decision will have to wait until after the summer break.
2. First I thought that after the preposition "from", only prepositionalphrases about a place can come. But this is not true.

ex) This decision will have to wait until after the summer break.

ex) Choose your wife from among your relatives.
3. Among the prepositional phrases that are governed by a preposition, theones about place can also be subjects of a verb.
ex) Under the bed is a nice place to hide.
It would be a great help for me if some of you native speakers of English will give me some feedback on my conclusion.
If you think there are exceptions to my conclusions, please write me a reply about it.