Thanks everyone for your repliea. And good advice NotJohn.
Well I opted in the end to force a page break for several of the images. On the Fire this looks perfect. On the other devices it looks just fine (I did a check). So all's good.
I had hoped there would be something to keep headers with images, but it's good to know it's not just me this is happening to, and that there's no quick-fix. I'm sure e-readers will be used to it, in this case
Thanks for all of the replies, they are much appreciated.
x