before you go messing around with the adjustments. The two lower arms of the three point hitch have two sets of holes for the side links to hook up to. maybe you have them in the hole that gives you more lift height.
the way I understand it the threaded rod adjuster is to limit the upwards movement of the hitch and the proper way to adjust it per the service manual, is to bring the hitch all the way up and to ensure there is still a little vertical play in the lower arms. I believe from memory that 1/2 inch of play is what is required.
the b7800 has a 1/4 inch valve control so the handle doesn't have to be all the way down he just has to hold it down until the arms are all the way down. One more thing, have someone push down on the arms as you hold the lever down because on mine they don't always go all the way down without any weight on them.