promotion and prorata problem

[Diploy]

When ever i enable prorata and i use fixed promotion amount it doesn't work too well because the promotion amount is not being adjusted to the prorata. In my case when i give the customer 470 dollar off and the prorata amount is 247 they get the server for free the first period till their next billing day.

 

How can i solve this? O is there no way around this issue.

 

Thanks