I am not sure what your trying to describe as an issue. Your not limiting your width of Photopost. I see nothing that is odd viewing your site. Your not using medium images and your main large images are max dimensions of 600 pixels so fine there.
Maybe turn off the next previous images in showphoto options in admin? Maybe set them to display in 1 row not 3 and to show left or right not bottom.
Just a few suggestions as I can only suspect your viewing your site with a small monitor.