Big thank you for this solution. Most photographers i know get a rather rabid look on their face, and traces of steam about the ears, when they see captions overlaying their photos :) -- it was a show-stopper for a web page rollout for the photographer i work for. I was about to wrestle with more css complication than i really needed to, and luckily did a web search first and found this.
It also worked for me to leave the default proportional setting in the main settings, and just change the "Slideshow's height" in the individual slideshow's settings. This was good for us, as we have other slideshows on the site that do not want captions at all.
Wasn't going to put page link, so as not to be one of those advertising kind of people, but then i saw the notice about including link "so others can see the problem", and hey, maybe would be useful to see a solution as well!