Are remains less likely to become fossils if they are covered quickly by sediment

No, they will still become fossils overtime, I'm almost certian

Assuming that fossils are to geology etc what "mummies" are to the Egyptians, then I'd go for being covered by sediment. The remains presumably take longer to decay due to being "smothered" as it were. And, maybe there's a higher chance that they can be embedded/imprinted in the rock to form the fossil.