Across Pay Period Functionality for Elements

Hello,

We have a requirement to tax across pay periods, every element has a different distibution amount that client want to apply, for the purpose of prorating the tax amount, when the supplemental element amount is high.

We have tested various scenarios but we don't understand how the system calculated the Income Tax witheld amount. What does the system understand as tax pay period, and how can we prorte the tax amount to be deducted from a payment.

The documentation does not provide a clear idea of what the system is supposed to do, so any guidance would be greatly appreciated.