My husband built a 20'-high tree swing, using 3/16"-welded-link chains to suspend it approximately 2' off of the ground. To our disappointment, pumping barely gets the swing going, with little height elevation. Even after being pushed to attain a decent height/arc (for a good swinging experience), pumping will not then maintain the height/arc. Is this a factor of having used heavy chain versus rope, or of the height of the swing? I remember a very high childhood tree swing with light cable suspension which similarly wouldn't "swing"; Grandpa always had to push us even when we were elementary school-age. Can a swing be too high?