Savings plan with matching based on service steps.

I'm needing to set up a Savings Plan with matching contribution based on the % of employee's contribution.

For example,

The employer will match 50% up to 5% of employee's contribution, and 25% up to %8 of employee's contribution.

Employees can have both Before and and After tax contribution but there is a limit on combined employer contribution.  I can't seem to get it to work using the limit on the Savings Plan.  It works when the combined employee's contribution is less than 8% but not more.  It just calculates too much matching contribution.