My CA 1901 J P Sauer & Sons / V L & D Knockabout sidelock has vertical sears. The pivot is very close to the middle (haven't actually measured the length of the two arms). The notch in the outer periphery of the hammer is engaged by the upper end of the sear. The front face of the trigger blade pushes forward on the lower end to release the sear. Seems like a very well thought out design to me & would which not be prone to "Jar-Offs".
My Lefevers also sears which engage the outer periphery of the hammer, as far as possible from the pivot. This seems far better than having the sear engage near the pivot where force is greatest upon the sear point.
