Calculate Overtime from a Custom field in Salary Structure

Hi I wanted to calculate Overtime from a custom field in salary structure assignment. Not from Base.

I have made a custom field - overtime base

that is added in Overtime Base salary component in the formula -

This salary component is referred inside the Overtime Type - Applicable Salary Components.
But when processing payroll after creating overrtime slip and submitting it the Additional salary is not created. Note the Overtime base salary component is reffered in the salary structure as statistical component. not part of earnings.

But when i change the Applicable Salary Components to Fixed Pay which is referred from base then the above process works. OVertime is calculated from the base value.