As you know DDO has peak times and off-peak times where the servers active population fluctuates. Mabar works well enough in peak with a reasonable time to activate the dragon fight. However during off-peak it can sometimes take several hours for the dragon to be activated.
So, instead of a flat turn in amount why not scale it based on server population each hour?
Or you could go one step further and base the scaling on players in delerahs graveyard so at the end of the event those still wishing to farm it can still open the dragon in a reasonable amount of time while the bulk of the server population has gone back to regular questing.
see it as dungeon scaling for events. you don't make a 2 man group have to wade through the same amount of mob HP as a 6 man group does. so it does seem fair to give players in an off-peak time less turn ins to farm