Although I don't know your exact use case, I am guessing that you are using some struct, enum or Simulink.Parameter type parameters. Such parameters are inlined by default because only built-in data types are supported as tunable parameters in generated S-functions. In such a case, you should see a warning in Diagnostic Viewer which would look something like
S-function parameter 'xxxx' can not be made tunable because its data type is not a built-in type
To work around it, you will need to supply individual built-in type parameters instead of combining them into composite type parameters.
