I believe that depends on how you have DBA/Evo set up.
 
If you have a PO Freight In (POFI) GL account and enter freight separately in AP-C, then Average Cost does not include freight. Reason being, there is a single separate GL account that POFI goes into, and you can't put the same amount in two places (i.e. POFI and your Inventory Acct).
 
There is a feature in DBA/Evo that allows you to add a percentage of cost to freight, and I believe that then goes to the inventory account and would be included in Average Cost. I'm not positive about that though - we used it on a couple items some time ago and stopped for some reason.
 
The last possibility (that I can think of) would be if you include the cost of freight in the per-unit cost when entering your PO lines in AP-C. It's pretty simple if you have just a single line as you can "Edit line" and just tab to the Total where you put it in and the per unit cost will be calculated for you. You can also manually split up how much freight you want on each line and then manually add that to each line subtotal, using the above method to calculate the total unit cost. Note that if you use this method and have one of the "Use last cost" options for entering prices on POs it will use this number that includes freight.
 
I believe you are right as to how Average Cost is updated, remember that "receiving" includes Work Order receipts.