Grid Images in Directory Press V.8.9.6

I have just updated to Directory Press v.8.9.6 and just working my way through some display issues.

I have my listings displayed in grid layout on search page and also on home page for featured suppliers. The grid images in my previous version would all display at the same size, regardless of what dimension they were uploaded as.

However in new version they are all different and there is significant white space around the images on the search page and underneath the image on home page. See screenshots

If I use CSS to try to fix I end up getting distorted images. See screenshots

Do I need to resize all of my thumbnails and if so at what dimension or do I need to amend the CSS?

Ideally I would like the images to fill the space like they do in the screenshots with the distorted images and have minimal white space wrapping around the images.

Thanks in advance.

.wlt_search_results.grid_style .frame img {
height: 600px;
width: 360px;
}

Can you advise what I need to do to fix this issue.