Featured image default size issue

Within this archive, I am facing issue of image size. I am using UB Post grid block, but the first image is appearing different and is cropped as well. This block is used in other categories as well but the issue is just here.
I need the image to be displayed correctly in a proportion of 1200 x 628 only, as other than that, the text will be cut in the thumbnails and it will look weird.

The page I need help with: [log in to see the link]