The rule of thumb is if the bend is a straight bend, there is no need to flute anything. If the bend follows a slight curve then yes, flute them. In the case of the seat ribs, only the bottom flanges need to be fluted because the bottom skin of the fuselage has a slight curve to it.
__________________ "What kind of man would live where there is no daring? I don't believe in taking foolish chances but nothing can be accomplished without taking any chance at all." - Charles A. Lindbergh Jamie | RV-7A First Flight: 7/27/2007 (Sold)
Verify the flange is square to the web, then flute the rib flanges until the holes are in a straight line. The web face will not be flat after fluting.
Steve