I can't be sure, but I suspect that what you are calling top-posting is the opposite. Top-posting refers to the sloppy practice of just pasting your reply ("posting") on "top" of the entire quoted email, rather than quoting selectively and replying point-by-point, as you're supposed to do.
However, bottom-posting's value is lost on the vast majority of people, so I don't bother unless it's someone I know will appreciate it.