ServiceOrder Billing - Bill Actual Amount From Appointment

Hi everyone, 

I have a created a service order billing cycle:

• Run Billing for: Service Orders
• Group Billing Documents by: Service Orders

In an appointment I have a service item with an estimate of 4 hours but the actual qty is 6 hours. After closing the appointment the item is transferred to service order for billing.

However instead of the actual amount of 6 hours the only 4 hours are billed when running billing. 

If I change the billing cycle to: 

• Run Billing for: Appointments
• Group Billing Documents by: Service Orders

now billing is moved to the appointment which will create multiple invoices which isn’t what we want. 

Changing the billing cycle: 

• Run Billing for: Service Orders
• Group Billing Documents by: Appointment

is not permitted by the system. 

Is there a way to to make service orders bill the actual amounts and qtys from the appointments? Or am I missing something why this isn’t supposed to work? 

Thanks