That's what I figured as well, Huvius.
This picture actually shows that the standing sight is dovetailed into the rib, while the 6 leaf sights appear to be on a different base, also dovetailed into the rib.
Hard to say for sure, though. The leaf's notches do no appear in ling with the standing sight, which might be lighting as well in the top-shot. They are very close, though.