It was suggested that I post here so it could be looked at as a bug:
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We project in 16:9 widescreen, iPads are 4:3 ratio (or something close) and the live view is set to have height of 100% with no overflow. This means that the right-hand edge is chopped off on all non-widescreen devices.
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If the CSS of the page was just changed to width:100% then this problem goes away (although, if their screen is too widescreen they now miss some of the bottom - less of a problem I suspect).
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I've made this change in the main.css file for our system and it works fine, though I'm not sure it's the best solution as it's still possible for some of the presentation to be chopped at the bottom.