Sales Commission saved search formula to reduce percentage on late payments

Please help to modify my saved search for the 3 following requests! :)

Please see my screenshots below. The sales rep earns a starting commission of 5% once a customer pays.

• I need to exclude the items that I listed in the criteria tab. Since my formula is based on the total amount at the header of the invoice, how do I re-write the Amt Eligible formula to be based on the amount of the total lines on the invoice (so that we can exclude those certain items on the criteria tab).
• Secondly, how do I write a formula that all aging invoices decrease by 1% commission per every 30 days past due (unless there was a 50% deposit made against that Sales order, then the commission does not drop). So basically each month the commission keeps decreasing by 1% until it is paid by the customer. This search will only show paid invoices, but we need this formula if the customer pays very late to figure out what the ending percentage is to be paid to the sales rep.