I've not experienced this. Looking at the mechanics of this: That area of the saddle is an inverted U section, held in tension by the steel frame, with downward force applied at the closed end of the U, which will result in compression forces (front to back) in line with the leather on top, and tension forces on the bottom (open end). So wrinkling would seem to be normal to me, if the leather is still stiff, with the "neutral axis" in bending, being partway down the sides. If the leather were soft, the sides would tend to flare out, losing some of the U shape, and you'd have more of a hammock. If that U section were reversed, open side up, in addition to being uncomfortable, the "edges" would then be loaded in compression, and not thick enough to resist that, and they would buckle. This is why U-sections are loaded in compression on the closed end and tension on the open end. Increasing the tension adjustment on the frame may help cancel some of the compression on the top side, but be careful, you may have sufficient mechanical advantage to cause damage at the rivets. Something in tension, the shallower the depression, the higher the tension, for a given load. So a looser adjustment will sag a bit lower under load, and more localized compression (wrinkles) on top, a tighter adjustment will be less sag under load, less compression, and a tighter, more rigid feel of the saddle.