I use the mudflaps too, can cut and use self tapping screws to secure them where needed.  Draper Belts work too.     You can also have the grain land on a scoop shovel and "overflow" into the auger too, that helps.   You can use anything shaped right so it doesnt get into the auger too.    On one auger I welded a piece of expanded metal over the very end of the auger(there are pipes that hold the safety screen) where the flight ends, it was kicking grain out from the end of the flighting.      A slight bend in the flighting can cause an auger to kick grain too.