Separate approval units for different approval groups within approval unit hierarchy

We have create separate approval groups for allowing phase submission by different business reporting processes.

However, the client has the requirement to have the approval process for one approval group to be at BU level and another approval process for another approval group at entity/BSV level. Since these are linked to same approval unit hierarchy to allow for editing data for one set of data while another set of data is still locked, how can we customise the entities included in approval unit hierarchy for different approval groups?