Hi @organisedgeorge,
I hope you are well today and thank you for your question.
To resolve the issue please use the custom plugin colorlib-divilab-plugin-113.zip shared in the following topic
https://colorlibsupport.com/t/feature-image-size-looks-wrong/#post-103745
Then regenerate thumbnails on your site using following plugin.
Best Regards,
Movin