Like using an ewheel, there are lots of ways to tuck/stump shrink. Here is a video that my son Kris did back when he worked for me and we were running up and down the interstates selling ewheels. It shows how we use the plastic hammer and also the height factor. Kris is 6-8" so this bag stand is pretty tall.
https://www.youtube.com/watch?v=mkaCJ5gC3jI