This seems like a very common issue, so I'm expecting there is an easy answer that I just didn't learn about in design school.

Essentially, if I have two or more parallel edges upon which I am running fillets, I obviously want them to have concentric fillets so that the wall thickness remains constant throughout. In other words, I don't want my fillets to have equal radii, I want them to have an equal center. I've attached images for reference.

A: several parallel edges to be filleted

B: Top view of fillet results. Red lines show equal radius fillets, blue lines show desired result.

C: L-shaped rib to be filleted

D: Result using fillet tool. Note variation in wall thickness.

E: Desired result (done using sketch fillets on a thin extrude, but this is not always possible.)