PRIMAVERA Managing Percent Complete

Hi 

I have a project which I split into subprojects. 

Example 2 project are activity type projects and are just different disciplines but actually make up one project schedule. 

The 3rd project is a milestone schedule linked to the 2 activity schedules.

I would like to know if there is a way to make the milestone schedule have no weight on the performance % complete calulation for the 2 activity schedules?

if I open only the activty programs I get 20% complete, if i open all 3 I get 3% complete.

This does not make complete sense since the milestones don't even role up percent coplete into the wbs like the activity schedules do.

I understand it probably weighs down the progress simply because it adds weight to the schedules, being linked to them.

Is there a way for me to keep this structure, but remove the weighting of the milestones on the activity plans?