Revenue forecast at project level, cost at lowest task causes problems

Summary:

The revenue forecast is at project/top task level. Cost forecast is at lowest task level. Once we have actual cost and revenue, and refresh the actuals the revenue amounts at the lowest task level are populated using the markup percentages defined in the respective resource rate schedules. So we have to change the forecast revenue amounts to 0 for the lowest task revenue amounts. Unfortunately I can't leave the rate settings section in the planning options blank, as that causes other error messages. What are the options to prevent the revenue forecast to be generated at the lowest task