I would like to know if there is a way I can select the relevance score as a column? So I can store for later manipulation
Also is there any way (for trouble shooting) to determine why a row got a relevance? or what words matched. For example when I use WITH QUERY EXPANSION I am getting results and I do not know why they match.
Re 1) yes. See the examples in the mySQL docs:
Re 2) No, not to my knowledge.
Check out the comments on the manual pages, there are several gotchas that may explain why one is getting zero results on a query that should return more than that.