Set blog post image to display *after* blog post title on post and page (Native)

I'm using the Native template exclusively as a blog. I use one image per blog post and want the image to display *after* the blog post title in all instances (blog post, blog page, etc.). 

When I first add the image to any given post, or when I am in "edit" mode, the image is displayed beneath the blog post title and matches the width of the text in the blog post. But as soon as I refresh the post, or navigate to the home page (blog feed), each post's image is displayed above the blog post title and much wider than the blog post's text.

How do I change this so that each blog post's image always displays beneath the post title and only as wide as the text of the post, as it does when I first add the image, or am in "edit" mode?

Can you share link to your site?