Usually it is in the centre of the biggest part of the pipe or just before the weld at that point. If it has a flat section there it would be in the middle of the band.
I watched John Perry do a test with numerous pressure fittings located thru out a pipe. Blocked off all but one fitting at a time. Attached a balloon and tested each location. Each balloon was filled with air as he went down the line. I have had pressure fitting in just about every part of a pipe. Front cone, rear cone and center. I could never tell a difference. A muffled pipe may have a different effect if attached into the muffled rear cone.