hi Robby
I didn't check the gallery layout before
but For shoing different sizes of images, you will find code such as "{$node.data_map.thumbnail.content.small.url|ezroot" Or "{attribute_view_gui attribute=$news.item.data_map.thumbnail image_class=small}"
the class is where you define small or large or medium , same is the place up in the first code line where i wroite small