Connect to ECC Function Module, Import Parameters are always Required

I'm connecting to a Function Module in ECC through IDT (4.0 SP9).

Once I drag the FUNCTION MODULE into the Data Foundation I'm prompted to enter a value for the input parameter that is optional in the ECC side; but Mandatory in IDT.

Is this by design or are we doing something wrong?

My goal is to filter the function module results on @boeuser variable; against the FM.