shall1028 - I've tested the files in iBooks now. File 1 (original file but shorter) still had the blank page after the cover image. File 2 (large cover image replaced with an image smaller than the screen of the iPad) had no blank page after it. File 3 (smaller image again but with width="100%" remove from the IMG tag) was also good.
Adjust - tried the magic number. I unzipped the file, got the cover image, changed it in Photoshop to the magic image size, opened the original ePub file in Sigil, deleted the cover original large cover image then added the new size cover (with exactly the same name) into the file and saved. Something weird happened - I ended up with a blank
before the cover image
and after!
I changed the image to 599x859px and tried again but had the same problem. Tried 550x789px and it was the same. Obviously I could find out what the maximum image size I can use without having a blank by trial and error but I think I'll just settle for a blank for the moment. The image shall1028 got it to work with was ~350px square! I also tested changing width="100%" to height="100%" in the ePub but I still end up with a blank.
Interestingly though, when I replaced an image in Sigil and resaved it the errors that I had been having in iBooks about entities had gone. I had been fixing that in Sigil by adding a space in the doctype, as described in this post on Indesignsecrets.com (
http://tinyurl.com/3blntgq). Why substituting the cover image for a smaller one affects this I have no idea
!