The KAB4 delivers a hell of a lot of BTUs. I've never run one on a keggle so I can't comment on whether or not the flames will come around, but they do saturate the bottom of these:
You can check for a leak with soap and water on all connections. Bubbles form if you're losing propane, but you would likely smell the adulterant they put in it to make it stink. Any chance you're getting a breeze blowing the heat away? It doesn't take very much to drop delivery significantly. I use a shield to keep the flame vertical unless it's a still day.