On landing, do your planes lawn dart or slide? If you're flying too nose heavy the plane will nose over when you try to slow down for landing, causeing the prop to take the brunt of the landing force. Moving the cg back will allow you to land slower and at a more level attitude. If you move the cg back, DO SO IN SMALL INCRIMENTS until you can slide in for your landings. Another benefit of moving the cg back is that you can reduce the control throws, which will reduce drag, which will result in a faster plane, especially in the turns.

Be very careful moving the cg on flying wings, a nose heavy flying wing will land like a brick, a tail heavy flying wing is a dangerous thing indeed.