Before adding the images to WordPress Flipbook – you need to check if the size of all images is the same. Then choose the right size for your publication – it should be proportional to the images size.
For example, you prepared images with size 600*400 px, choose this size for height and width of publication or smaller, but always keep the proportions – e.g. it would be 500*333 px.
For Area Width and Height – set the sizes a little more than your publication size. It will make the look of your WordPress Flipbook better.