Withholding Tax exemption scenario

Hello,

Please help me with the below scenario.

WHT say example 1A maintained as WHT rate 0.00% and indicator for calculating withholding tax according to formula is selected.

And WHT 1A with WHT Country say US maintained in table T059FB as 25%.

When I post vendor invoice with WHT 1A and WHT Country US, WHT 25% is calculated correctly and posted.

But, when I add exemption in vendor master data (ex: 50%), WHT is not calculated for the Invoice.

Kindly let me know do I miss any configuration in calculating WHT.

Thanks

Amar