A bit of left margin will be no bother.
The look of the avatar + meta section being one item is not how the HTML layout goes. The structure is:
( [Avatar] [ <Meta> <Body> ] [Gutter] )
So it’s easy to push the avatar around, but tricky to push the avatar and meta around consistently.
The default style (with the meta along the top of the post) copes much better with a narrow window, but wouldn’t it be jarring to switch between the two?
- Note: Gutter still needs fixing but I don’t have time right now