Had a chance to ask that question of Virgil Headrick one day when he & Coop were on a eastbound job freight stopped for water & lunch. I think they had a 490. Anyway, his comment about firing the "chippies" was that for him, he would "hog trough 'em". One to three scoops up on the side sheet and let it roll down to the sides, keeping the back corners filled. Different strokes for different folks.