Gil,
You are correct in calling out my typo error, but depending on the flange, the bend radius and the rivet size, there may not be much margin for error. Some of the flanges I have had to work with were not 5/8, plus with a fairly generous bend radius. The flat was significantly less than the mold line.
I understand the drawing as showing the side of the rivet head beginning at a minimum point .030 from the edge of the bend radius.
By picking a line that allows a little extra margin than the minimum on each side, I am still in good shape if my drill point errs a bit, or God forbid, I screw up the rivet and have to go up a size. It has happened.
Centering the rivet hole, more or less, on the flat, seems to work best for me and meets the minimums with a little to spare.
Dave A.
6A build