Sizing images for Flipbox

Hello, I have just come across the excellent plugin by codelight. A good few options for presentation of information. The effects are very nice.
However I cannot appear to get the images to size to the correct proportions. How is it possible to control the size of the images on the front and back side of the flip box?
I have set a few up and tested this but the images appear to default to a size which crops the images to a landscape box whereas I am trying to use portrait images.
Do images have to be sized to fit to make this work? I was quite excited at seeing these effects and would like to use them but the issue of the sizing of the images is a bit of an issue. Even the IMage Size within the FRont and back pages tabs does not appear to cause anything to happen.
Is there an issue with this at all?

Help and support from anyone who knows how to get the images to fit better would be most appreciated.

anthonyod