Hello,
Actually the height of the product box depends upon the inner content. So if you want to display the same height then you can use the same size for all the thumbnail images and inner content must be of equal length like product name.
Also we have provided “Masonry grid” option for this purpose. This option draws a border so that rows are of equal heights. There is no other option to display the thumbnail images of the same size.
You can enable the “Masonry grid” option from theme settings >> shop >> PRODUCTS STYLES.
Best Regards.