I find that broad beans can go in deep, say 2in/5cm or more, but everything else I sow does better not too deep = what I say in the books, a dusting on top equivalent to twice the depth of the seed’s thinnest cross section.
So lettuce is v thin and needs almost nothing on top, in fact mostly I simply leave it on the surface uncovered, but in the shade to stay moist until germinated.
