SSRS Dataset Filter expression query

I have an SSRS report which has a simple dataset and accepts two date parameters, and filters the results based on a Position parameter. The Position parameter filter is:

Expression: Position
Operator: In
Value: [@Position]

I have now been told that each position has a few other aliases in the database against the Position column. i.e. For a Position of "Contractor" I now also need to return "Consultant" records, based on the same field. Note, only one Position can be selected at a time.

I imagine I have to update the Value expression above to do something like:

- When @Position in "Contractor" also return rows where Position is x, y, z (I am happy to hard code these)

I have about 10 Positions each with one or more aliases - can someone help guide me on how to set up the expression?

Thanks!