The BSF grubs will only be on the top of the pile if there is food there. If I don't feed them for a day or two almost all of them will go below the surface in search of food.
The size of the mature grubs and can vary quite a bit and I've seen many pupae that were 1/2 inch long or maybe even a little less. Of course all of the mature grubs will stop moving after they pupate and most likely you'll start to see the adult BSF emerging in several days. I'm recommending only about an inch of sawdust because if it's too deep it can be hard for the newly emerged adult BSF to climb out.
I'm looking forward to hearing that you have small BSF grubs in your BioPod. After that your colony should expand quickly.
