How to make Supplier Registration process create site assignment for main BU only?

Summary:

Checkbox "Autocreate site assignments for spend authorized suppliers" is checked. However, since we have setup Service Provider Releationships between the main BU and other BU's (for using Agreements ONLY! we dont have a cross BU procurement) - the process creates Site Assignments for ALL BU's and that is wrong.

Any idea will be appreciated, thanks Avner

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