CSS Fix for Small Category Images Nearly Working

Hey there,
I’m working on a few CSS fixes for image thumbnails that are too small due to dimensions or otherwise. This particular one is for the Big Grid on Category pages. The CSS is –

a.td-image-gradient.td-big-grid-overlay, .td-big-grid-post .td-module-thumb img.entry-thumb, .td-module-thumb{
height:100%!important;
}
a.td-admin-edit.td-image-gradient.td-big-grid-overlay{
height:auto!important;
}

Example at http://www.xposy.com/literature/

This is working to a point. It seems to drop off at the smallest screen dimensions. Probably down to the wrapper?
Anyone have an idea of what to add?

Thanks!

thanks Sean .