Quick reference list of how to bury, or not, different kinds of seeds:
Don't bury: lettuce, allysum, thyme, anything thats seeds are as tiny as dust or flat as paper. Water them in and protect them from birds.
Cover or not: things that are the size of coarse ground pepper. Things like: mustard, kale, basil, tomatoes, peppers, onions. Tamping them gently will help them. A thin layer of vermiculite will help, but isn't critical.
Cover with a thick layer of vermiculite: cilantro, chives, dill, parsley. Anything that grows in a clump.
Cover with vermiculite and then cover with another tray: sage, microgreens.