I don't have any particularly insightful advice for you. Humidity is just water. If you have too much in there, take it out. To do that, you could swap out your water bowl for something with less surface area. Less surface area = less evaporation = less humidity. If that doesn't work, you could change the substrate that you moistened when your bp was in shed with something drier. 73 percent isn't that high, so you shouldn't have to do much. I think where you have the hydrometer probe is fine.