I have to agree with 400NE. When firing a double rifle the leading hand should encompass the forend and grasp the barrels. The trick is not to obscure the rib and sights. Its not like shooting off a standing or seated rest. However, a rest is useful for regulation. But even with the rest the regulator will grasp the barrels and rest his arm. The final elevation on the sights needs to be accomplished while standing and grasping the barrels. Its kinda like the difference between a sling and no sling on a bolt rifle.
Phil