Need the ability to invoice for a project by hours by tier. Ex: The first 100 hours of the project each month are billed at a rate of "X". The next 20 hours are billed at a rate of "Y" and anything billed over 120 hours are billed at an hourly rate of "Z". When the project hours are billed and a user tries to modify the invoice, it drops the link between the project and the invoice for billing purposes. There needs to be a way to make adjustments to the billing rates (add/modify the hours) the same way you can make adjustments to an invoice for a sale price on goods.