Boost the custom pane height
The maximum of 450 for the RequestedHeight element in the schema manifest is not quite large enough. There may be scenarios where the UI needs to cover the entire Reading Pane. Form Regions in the Outlook client already support a complete replacement option for some Outlook items. Add-in Express also has this feature for their Advanced View and Form Regions. Maintaining consistency would be best for all design scenarios and migration from other platforms.