When running the K9 Power Seamer over pre-formed panels the result is a boxed or square seam instead of a double lock standing seam. The seamer may also pop off of the seam.
When the number 3 roll comes along the seam it applies pressure to the female leg. The female leg, in turn, applies pressure to the male leg and they both bend together around the point shown on the right.
When the male leg is not long enough the female leg does not have sufficient leverage to bend the male leg. Instead it will bend around the outermost tip of the male leg as shown on the right.
Here is an example of correct lip dimensions for proper seaming. The male leg has sufficient length and the third roll will have enough leverage to bend it.