Currently Compress Prepayment option can be set on the document level in Sales Order and Purchase Order. However, for companies that use sales prepayments it is important to have the items listed also on sales prepayment invoice. So that the ultimate customer would understand what the prepayment is about.
Sales Confirmation + Sales Prepayment invoice is not considered as the best option, in order to provide the details.
Please consider moving "Compress Prepayment" from sales/purchase order level to Sales&Receivable and Purchase&Payable Setup. From the user perspective, it is very inconvenient to remember each time to remove the checkbox from sales/purchase order to get the document right. It should be a resolution made by Accounting policy, not a single user.