I am not familiar with 3D tracking so take what I say with a grain of salt, but I think I might know what’s going on.
The emitter position in particular is only x and y, there is another option for z position…
If you can develop an expression to link the x and y position data with the corresponding points on the tracking data, then use another expression for the z position to the z tracking data.
If it sounds confusing, it probably is so I recommend Andrew Kramer’s 3D Light Streak #2 Tutorial found at: https://videocopilot.net/videotutorials/nano2/