Payroll Calc Setup -- Local tax districts

We are a service company and we work in the KCMO local tax district multiple times a day, along with locations in Kansas and Missouri. We have been informed that the local KCMO tax rate of 1% on wages should be on adjusted gross wages but we are being told that it is not possible to set that pay calc up in Sage 100. We currently have one set up for 1% of gross income. Has anyone ever run into this issue? If you have, how have you resolved this to calculate correctly?