If the MostRecentItemsPercent property's value is -1, the actual setting is specified by the BarManagerProperties.MostRecentItemsPercent property.
The BarManagerProperties.MostRecentItemsPercent setting is available in a BarAndDockingController: the default (DefaultBarAndDockingController) or a custom one (Controller).
Any value except for -1 assigned to the MostRecentItemsPercent property overrides the BarManagerProperties.MostRecentItemsPercent setting.