I wish I knew ... it depends on the website. I suggest asking Lau or Sinsboldly. The way I understand it, "cross-posting" involves responding to a question from one thread with an answer in another.
Unfortunately, there is no global standard for cross-posting, or even "spamming" a thread. On one well-known composer's website, posting only "I agree" is considered spamming and is grounds for a warning from the mods, with repeated instances resulting in a complete ban of the individual from that website.
(EDIT: I'm currently running a 102°F fever and trying to type in dim light ... I don't catch the spelling errors until I've re-read the post a few times.)
_________________
The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.