Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so each of the 8 parameters is already documented in the schema. The description adds the linking model ('stand alone or link to a person, a company and/or a deal'), which reinforces the relationship among person_id/company_id/deal_id but adds little beyond the schema. Baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.