-7 wing leading edge 'glitch' ?

-7/-8 builders,

Has anyone noticed a slight dip about an inch above & below (back of the
actual apex) the rolled leading edge of their tank skins & leading edge
skins?

While handling one of my cleco'd tanks, I felt the dip, & thought I had
somehow dented the leading edge. On further inspection, the 'dips' are
slight valleys running the entire length of the LE & are identical on
all 4 skins. On the top side, it's about where the 2nd rivet will be in
each rib. It seems unlikely that it's due to the ribs, because there is
no difference in the valley mid way between ribs.

I might be good at messing stuff up, but I ain't THAT good.

Thanks,

Charlie