Vict
Did you notice on the one you list as having too much space, if you select the second pic - that pic moves down and the spacing is consistent with your one pic product.
My "guess" is it may have to do with the size of your images that are uploaded - they may need some tweaking. Compare them for originating size and see if that will make a difference. Check to see if there is white space in the first pic at the bottom that may be causing the issue. OR there has been some tweak in the code that make multiple pics act differently in presentation.
Lee