Why do some non-precision approaches have stepdown fixes after the final approach fix? Some of the non-precision approaches have a stepdown fix after the final approach fix. My understanding of a stepdown fix with an altitude restriction is that it is to keep you clear of obstacles before continuing your descent right? However, why does it so happen that some stepdown fixes are after the final approach fix rather than let the final approach fix be the "stepdown" fix of an approach?
Take a look at KPRB VOR Rwy 19:



There is a stepdown fix after the final approach fix. Now look at the terrain around the airport. You can see a bunch of small hills around the FAF. In order to provide adequate terrain separation and get you low enough to land, they need a stepdown. You can also see this on lots of non-precision approaches where the approach minimum is lower if you can identify a point past the FAF. 

If you are interested in how they decide to include a stepdown fix, check out FAA Order 8260.3C TERPS, Section 2-6. Final Approach. Lots of formulas but the gist of it is they have a required obstacle clearance that must be met and maximum descent angles. Sometimes they need a stepdown fix in order to make the approach work.