It's been many years since, but I made a lot of flights with my 29/40-120 casing using F and G reloads. Back then the common wisdom was to position the igniter at the front part of the fuel grain. When I would build a motor I would first put the nozzle against the fuel grain, insert the igniter and push it so the end was flush with the front of the fuel grain then I would bend the wires over at the back of the nozzle. Then take the igniter out and set it aside while building the motor. Then I could put it back in and know it was going to the right position. I never had a problem with incorrect delay time, or chuffing on the pad. These were with igniters made by our motor vendor, not the copperheads.