[Cpt.Crashtastic]

{math equation="((x - y) / 2)" x=$config.Appearance.simple_thumbnail_height y=$subcategory.image_y}

I used this to set a top margin so random sized thumbs were vertically centred. Couldn't do it with CSS. Maybe if you called your own version of product_thumbnail.tpl you could size your images from there.

Hope this helps a bit