How to prevent the thumbnail image on the index page from pulling through on the project page itself?

Site URL: https://www.angelodonnell.com/projects

Hi!

Do any of you know how to stop the thumbnail image of a project to carry on pulling through on the index page, but not as a banner on the project page itself in theme: Artesia?

OR how to allow the full image size to pull through on the project page, but still be automatically cropped in the thumbnail on the index?

Thanks so much in advance!

Best wishes,

Dom