Hopefully I am reading this right. I just got done getting my wings flight worthy and had to restudy this myself. The reason, I believe, the flush side on on the outside is because of how the bearings might fail and which way the aileron will move if they pop out. The large washer on the inboard bracket prevents the aileron from going outward, but it would end up sliding inward some, thus the need for flush heads outboard(?). I doubt it is very likely for this to happen, but I also suspect that is why the per plans gap is 1/4" to the flaps.
Now that being said, I had to drill out the upper one of those rivets and make it a double flush rivet because my aileron needed to be positioned a bit more outward to make room for very difficult to fit flaps. I had less than 1/32" clearance to the shop head of the rivet, so I decided to make this change.