Hello,

That will depends on the site template, the strucure, and the size of the main container.

In all cases, it's always better to have an image a bit larger than the display block size. (it has a better rendering on high definition screen).

It seems you have a pro subscription, so if you open a private ticket with link to your site, i can check it and give you some tips

www.joomlic.com/support

Best regards,
Cyril