crater sizes
One can get smaller craters on earth (and Mars also) if the impactor breaks up in the atmosphere. Hence the Henbury craters were there are ~13 between 6 and 180 m across. Secondary impacts can also create smaller craters.
The composition of the impacting body is also important. Iron meteorites should survive entry better than carbonaceous chondrites and also retain a greater velocity because of their higher ballistic coefficient. All the smaller Australian craters - Dalgaranga (24 m), Veevers (70 m), Boxhole (170 m) and the Henbury group are formed by iron meteorites.
How do you determine the condensed atmospheric thickness?
Jon