I've been using field parameters to toggle between which field is displayed in a matrix. This works great when there's only one level of rows to display. However, when I include an additional row level to my matrix, changing the field parameter will reset the drill level to the highest level every time. This leads to poor user experience for the audience, as they have to click to expand the rows every time.
At present, the dynamic field conversion of the field parameter cannot be drilled to the last level, but only to the first level. If you have this need, you can mention your ideas to the Ideas forum. If a feedback is high voted there by other customers, it will be promising that Microsoft Product Team will take it into consideration when designing the next version in the future.