Slider Image Size

Hi

When I look at the slider on a category page I can see that some of the original image is cut off when compared to the image for the post below it e.g.:

http://www.glutenfreemag.co.uk/category/eat/

Is it possible to have the slider image display exactly like the image for the post? Ideally I would like the whole image to be shown.

Also, what is the recommended size of picture to upload for featured images?

Many thanks in advance

Martin

I think the image sizes are still found in the theme docs, as so:
https://forum.tagdiv.com/modules-and-blocks/