Issues with thumbs(featured images)

I am using your stupendous theme and loving it. However I have run into an issue. In the grid based homepage, my thumbs seem to be misarranged.
I am using external featured image plugin along side the usual featured image using media library.
The Images appear to be different heights. When I see the thumb-medium specification in theme-functions.php, it is 520*245, but that doesn’t seem to be the size here. Can you please help me sync the two types of featured images. I was able to sort the issue out in side bar, but post-list solution evades me.
I am using this extra css to control the height, but this seems to affect images pulled from external images plugin and not the ones using legacy featured images.
.home .main .post-list.group .post-thumbnail img{ max-height: 160px; }

Please note that I don’t intend to fix the height at 160px, It should best suit the device.