How to define a simple parameters table when using a shared Power BI dataset ?

The parameter table has to live somewhere and I don't think there are any reasonable options other than in the shared model or in a local model.

My general heuristic for this is that if it's a parameter table that will be used in more than one report, stick it in the shared model for the sake of unification. If it's a one-off thing that isn't likely to ever be used in any other report, then maybe do it locally.

Note that it's possible to create parameters that are more general than case-specific to reduce clutter. For example, you could create ThresholdParameter rather than SalesThresholdParameter and use it for things other than sales in other reports.