[Suicide Junkie]

There is no way that a planet could help a moon hold on to atmosphere. Jupiter's moons are just big, thats all.

Tiny planets would almost all be 'none' atmospheres (as well as moons)

Small planets would usually have atmospheres, and some of the biggest moons would be small planet size.

Assuming Earth-mars-venus type planets are the small end of medium sized (SE4 homeworld size)