anytime you use something deep or something they can get into, they will pile up and drown those on the bottom. the screen came off my poultry feeder once and the next day the jar was 1/2 full of dead bees. looks like you had a pile on in your feed dish.
use something shallow. put rocks or something in so that bees can crawl out. make sure it's big enough. that dish doesn't look like it is. you might try the poultry feeders. you can put a lot in them and then not worry about them. don't know if they'd fit in a TBH, but you can look at them in feed stores.