Are you using a mixed-aspect-ratio grid? If so, the only way I've found to optimize it is to use different description bubble graphics depending on platform. It seems that the Roku 1 has a much wider top margin for that grid type than the Roku 2/3. If you take a screenshot with the default graphic, you can use that to figure out the proper sizing and placement, but it's still a headache.
My Channels: http://roku.permanence.com - Twitter: @TheEndlessDev
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