Exhaust pipe length.

When fitting new exhausts I have noticed the amount down pipe that fits into the silencer seems excessive, I would have thought a couple of inches would have been enough!....surely it would be more efficient if it was shortened, I have seen this from more than one supplier, anyone else experienced this?........

Not sure about efficiency, but the farther you slide the pipe into the muffler, the closer the end of the muffler is to the exhaust valve and the quicker those final negative pressure waves get to said exhaust valve.. The junction where the cross-section gets larger is effectively the same, so that pressure wave would remain the same, timing-wise.

The diameter of the exhaust pipe does not change the length of the standing wave within it. It simply changes the magnitude of the pressure pulses. If you have a different pipe length, it will change where in the rev range the power band occurs. You probably would not notice a difference.