Managing user permissions with multiple roles

I have a table for submitting and approving change requests.  My table has a submitter role and multiple user roles (one for each approval function so that their access is limited to modifying only the appropriate field).  Due to some complex approval requirements, different request types have different approval requirements, so when the form is submitted, a form rule changes the status of certain approvers to "not required."   In order for this rule to work, the submitter role needs modify access to the approval fields.  That works fine except for the few cases where someone in one of the approval roles also has a submitter role.  In this case, the access permissions "overlap" and these users have access to change every field.  Does anyone have suggestions on how to manage this?  I've tried having different forms for different roles, but again the overlap between roles prevents this from being a workable solution.

Thanks in advance!

Chuck