Its a question of fact if a customer arrangement is a Sales Order or an Invoice - the financial reporting should then follow the facts.
A 'sales order' is a customer request for future action. The sale action has not yet occurred and there should be no Cost of sales activity yet.
Invoice means the sales action has occurred - and the costs of the performing the sale have been incurred. Future payment for past sales is normal AR - it should be on the financial reports.
If you want to report 'cash basis' do so in report settings - not in how you record sales.
