OK so a better option then creating a new Header Element for each Page.
Select All of your current Header Elements and under Bulk Actions select Edit. And click Apply.
In the modal change their Status to Draft.
This will temporarily disable all the Header Elements.
Now create a new Header Element.
In the content add the <!-- page hero -->
comment.
And set your Padding as before.
Now select Background Image > Featured Image.
Below this you will see this: Disable Featured Image
appear, check that.
And set the Display Rules to Pages > All Pages.
Then edit each Page and in the Featured Image meta box add its Image.
This should work for all your Pages.
If that works then you can delete the individual Header Elements you drafted before.