Hi Wm,
That example isn't responsive, so they've just fixed the height on it. Responsive slideshows only know their height once they're displayed. The 1x350px image seems like a niceish workaround.
The responsive box idea is the route I was going down. It needs to be done with pure CSS though as the box needs to be 'present' as soon as the page loads. I found a few different ideas (tried maybe 8 or 9 approaches) but none of them worked well for me.
Regards,
Tom.