The pilot reported that during landing, the airplane veered to the right, which he corrected by using left rudder. The airplane again veered to the right, and as the pilot applied left rudder, the right main wheel came in contact with soft mud and the airplane nosed over. The airplane sustained damage to the wings and the left flap. The FAA coordinator interviewed the pilot. The pilot's statement was that he is a certified flight instructor who has instructed in Citabria's and usually sits in the rear seat. On this flight, he was taking a friend up and decided to fly from front seat. He stated that he was concerned when sitting in the front seat that he could not fully reach the rudder pedals (he is 5'6'' tall). He considered getting a pillow to help him sit forward but decided against it. He stated that his inability to apply full left rudder was a factor in loss of directional control.