Conventional wisdom (and you can take that for whatever its worth) says that you don't really need to worry about "air space" or "breathing." Now, I don't care if you do or don't, I just wanted to throw out the "flip sides". There are reasons to pack tight with sawdust and wax over the top, like keeping pill bugs and slugs out of the logs, to also consider.
Your mileage may (always) vary.
Also, look up the Totem method, it is less effective for slow stuff like shiitakes, but popular for oyster mushrooms. If you can't find info elsewhere, there's some on Field and Forest's website.
As for me: just found 2 shiitake on logs in my tree-yard, all covered in sand and grit. Time to move my logs to the north side of the house for fruiting......