Upgrade Setup Fee

[vmm]

Hi,

I'm trying to create a setup fee to component upgrades after a client has already made the initial order of the main product.  However, I don't want that setup fee to apply if the client chooses that component during the initial order. 

-I.e. client orders Server #A and chooses HDD upgrade #3, total price: Server #A + HDD upgrade #3. 
-If client chooses not to buy  HDD upgrade #3 upon initial server purchase, but at a later time, client cost:  HDD upgrade #3 + Setup Fee.   

So my questions are the following:

• What is the difference between "Full" and "Price Difference" as seen on first attached screenshot and/or here: http://snag.gy/8ugaH.jpg
• Once choosing one of these options, where is the field where I enter the setup fee for when the client BUYS THE COMPONENT AFTER as opposed to if the client buys the component during initial product order?  See http://snag.gy/d7Qif.jpg and/or second attached screenshot, i believe this applies to the setup fee applied during initial purchase, which I do not want to charge for.

Any help would be greatly appreciated.  Thank you.