How to view applicable WHT on invoice when Calculation Point is Payment

Summary:

Invoice users require the ability to see the calculated WHT on validated invoices, even though the calculation point is 'Payment'.

Content (required):

We are applying withholding tax on some Payables Invoices, based on the Supplier withholding tax group. The Calculation Point is 'Payment'. Our payables users need to verify at Invoice Validation time that the applicable WHT will be applied. But it looks like this detail is only added to the Invoice after payment is made. How can the invoice entry user be confident that the correct AWT will be applied? If it is only shown after Payment, and it happened to be incorrect, it would be too late.