Note how the ribs DONT fit into the skin! You need to flute the ribs to allow them to fit. Put two creases at 1 o'clock and 11 o'clock then flipped it over and put a crease at 12 o'clock.
The rib will then fit in perfect.
Tried radiusing the rib, but didn't like the way it came out. Threw rib away and ordered new one. $5.10 I think I can live with that.