I've only ever seen the wings have the tapered recess top and bottom, though have lived long enough to learn that there always seems to be a remote exception somewhere. The reason for the tapers is that there is a lot of stress/load on these components and the pieces that bolt together with them. Don't want any sideway movement. The perch bolt has the matching taper on the head, then at the bottom you either use the lower shock mount bracket which has the same taper to mate with the bottom of the wing or that conical spacer and the flat nut in it's place. Your last sentence sounds like you're planning to mount the perch bolt upside down? If so, not a good idea from a safety standpoint.