Post Hero image of Mellow Theme

Hi Team,

In Mellow theme, Post Hero takes featured image of the post as the background image. How can I use a custom image for each post? If I change Post Hero setting to custom image it will be applied to all posts. But I need to have different background image for different posts.

I tried creating a separate Post Hero element for each and every post with its own custom image. But is it practical since I have to create a post hero element every time I publish a post? Is there a limit for the no of post hero elements?

Thanks
Chamika