Dawnguard goes above the shield because there's not (normally) a bow that goes there already. IW does add the Silver Hawk Bow, so it could work. Dwarven crossbows actually go behind the armor, making it impossible to see on full display. Most other display have the trident or double axe go in that spot. On a different subject, I would, if I had the talent, make a patch that rearranges the gallery a bit. The Ring of Khajiiti should go in the Daedric Gallery instead of the Jewelry case, the Madness, Amber, Seducer and Saint armors should be in the Armory, otherwise the Daedric armor should also go in the Daedric gallery, all of the Sheogorath things could be grouped together in that lower hall instead, which would open up a lot of free spaces for other add-ons. Add-ons like the Ada Bal from the VIGILANT mod which, being the only real "daedric artifact" included in that mod, should probably be in there instead of the Vigilant Hall. Also perhaps an expansion of the Natural History wing to include some of the more lore-friendly Milahil creations.