Customer Down payment with billing plan

Hi Experts,

i am trying to do customer downpayment with milestone billing ,for this iam facing issue in the billing level

Billing Plan

01 downpayment request      40%     40 usd     FAZ

02  closing invoice                  60%     60 usd     

in this i am creating sales order and i did billing for downpayment and posted to accounts through F-29 till this its working fine ,but when iam creating closing invoice that time billing value shows 00,000 ,i triyed somany ways but not find nay sloution .

And another issue

01 downpayment request      40%     40 usd     FAZ

02  delivery                            50%     60 usd     

03  closing invoice                  20%     20 usd   

in this way its should be allow 100% only but sales order allows 110 % percenatge also  SO not showing error message also ?

Its gald to any body post the solution for two issues ....

and suggest

how works header level billing plan? what are the settings require for that?