Sherman - thank you for your reply.
I discovered leaving the default /
was the way to go.
I am a novice when it comes to HTML and CSS, but I have learned a bit through trial and error. What is weird is that I compiled a similar book with the older version of Sigil that required manual chapter breaks (one long document) and it came out as a perfect epub and mobi, with the images appearing at the beginning of the chapter. But with the current version of Sigil, the same CSS and code (I presume) results in the page breaks following the image and preceding the chapter. Argh.