Legends of proportion dots: Ability to control the sizes that appear in the circle-size part of the legend

[KelleeKoenig1]

I often create proportional dot, and proportional pie chart maps. Currently, the legend gives 3 sample circle sizes, but the associated units are often...unintuitive. Just like we can adjust and fix the units for a scalebar, it would be great to specify what dot values we want in the legend for the circle part.