Payroll deduction as percentage of net

SOLVED

Canadian Payroll - I cannot figure out how to set-up a garnishee code that calculates on percentage of net pay. Is this even possible? I've tried every possible combination of Calc Bases and "take deduction before". I can get it to calculate tax correctly (as in the deduction is non-taxable), but the actual deduction continues to calculate as a percentage of gross. I'm assuming there is no way to use "percentage of base" as the employee calc method for the deduction?