Milestone Billing

I have created one Milestone billing and defined four stages, as Advance received , Project stage 1 , Project Stage 2 and final Settlement. For the Advance payment i am using FAZ as the document type and for the rest of the stages i am using F1 as the billing document as this is order-rel-Billing.

NOw when i am creating a billing for Advance say 10 % of the total value i am able to create the down payment Invoice FAZ.

Now when i am creating a INVOICE F1 for the project stage 1 60 % , the system is picking up the total value of the order which is 561,800. Infact this total value has been broken into two parts, 60 % and 40 %

which is 337,080 and 227,720.

Also i want to know what will happen for the final settlement invoice as this is the fourth stage for which i don't have any percentage defined

it like

Stage % Doc type Total value ---561,800

Advance 10 % FAZ 56180

Project St 1 60% F1 337,080

Project st 2 40 % F1 227,720

Final Settlement F1 No values

Plz Help as why the system is creating invoice with full value of the order for Project st 1 that is 561800

and how the Advace payment will be settled against the Final sttlement.

Also let me know whether while creating the individual invoice for each can i change the value of the invoice.

Cheers