Hi In Ax the effect would be the same but happens at 2 different points .
Step 1 When u invoice the respective tax gets calculated and payable shows as 1120.
step 2 when make payment withholding tax gets deducted and net payable is 1100 only .
In one my implementation where client insisted that invoice should show net payable wee have customized the invoice to show this .
Total invoice amount 1120
less WH tax 20
Net payable 1100
Hope this helps