Fillet a portion of a slot

Hello,

I am trying to make a radius (I want it to be 90deg of a circle) on just one side of the slot but can't seem to get this to work easily.  With tangent propogation on when I select the edge I want it propogates over the entire back face and with it off just nothing works.  I attached an image of what is happening and what I want to do.  Looking at the top left picture I want the left side to have a radius but then the right side to remain flat.

SolidworksParts And Features