Chain tension issues – 10 speed

first build so it’s probably something very obvious, but I’m having chain tension issues on the smallest two cogs. it doesn’t appear like the B-limit screw is able to seat properly on the stop tab, even when fully threaded and there’s a lot of play around the derailleur hanger bolt. what am I missing here?

Shimano Deore XT RD-M781-GS (Medium Cage) Silver Rear Derailleur 10 Speed

SHIMANO Deore HG50 10 Speed Mountain Bike Cassette 11-36T

10 speed KMC chain