I have checked the shop page. Now the grid item has min-height: 1px; It means that there is no limitation. For this design style, the image height determines the height. So you need to upload images of the same size and the same proportionality. It is not possible to set fixed hieght for image element as short images would be stretched and blured and big images would be pressed.
I don’t know which settings you are talking about (min-height: 1px). All what I’m trying to do is, if a thumbnail height exceeded 300px for instance then it should be scaled proportionally to fit the max-height, got me?