Array function on offset(width)

[MauriceSmit]

Hello fellow Excel specialists,
I am currently creating a financial model and one of the main tables will be the 'cash flow statement'. For this, I am currently hitting a wall on the formula I intend to use for Accounts Receivable (and Accounts Payable).

I am trying to capture the amount of AR/AP per month. I know how to calculate the value step-by-step, however I would like to use a single formula to calculate this amount.

In the attachment I have a simplified design of the overall model (saves precious disk space).. The first table on top, shows the 'input' area (the rows are variable by the end user). The second table shows the manual steps to come to the Accounts Receivable, with a total below. The orange highlighted cells is my first attempt on re-creating this value using a single formula.

I currently use an {sum(offset;x;x;x;QQQ)} formula, in which the 'array' part of the formula comes from the offset-variable 'width'. However, the formula only anticipates on the first Accounts Receivable setting in the list; neglecting the other values.

I hope anyone can help on this one

(attachment)
http://www.helpmij.nl/forum/attachment.php?attachmentid=146569&d=1327915738