Virtual Dataport will delegate the SQL Stored procedures to underlying data sources as is. Virtual Dataport cannot modify the number of parameters defined in the stored procedure. So, it can only call the Stored Procedure with 2 parameters as the SQL Stored procedure and retrieve the data from the source, then perform the third filter condition in Virtual Layer.
To make the third parameter to be delegated to the source I would rewrite the stored procedure with three parameters so all three parameters can be delegated to the underlying data source.
For more information, you can refer to the following Knowledge base article [Creating views on SQL Server Functions and Stored Procedures](https://community.denodo.com/kb/view/document/Creating%20views%20on%20SQL%20Server%20Functions%20and%20Stored%20Procedures?category=Data+Sources) and [Does creating a base view from query mean the query can not be delegated?](https://community.denodo.com/kb/view/document/Does%20creating%20a%20base%20view%20from%20query%20mean%20the%20query%20can%20not%20be%20delegated%3F?category=Data+Sources).
Hope this helps!