Ok, thanks so much. Firstly, I learned that /edit permits me to view the raw markdown of any post. That might come in handy!!

The other thing is I think what is happening is that in a comment reply the image is not rendered the same as when in the body of a discussion post. Which is fine, but explains why me even doing a copy pasta of hj's markdown still results in a small image that only expands when I click on it.