@crutledge
Wonderful. Your code works as mobi and epub for me now.
I don't know why but I do know how.
Each line of my poem was a separate <div> it is now one div with line breaks.
Two things then needed to change, one or the other is not enough.
1. Put the whole <div> inside another <div>
2. Style each line with text-indent using a <span>
Many thanks.