Hello
Brainstorm uses 4 integration points for each MEG sensor (corresponding to the 4 corners of the Elekta magnetometer or gradiometer).
However, if you use only one point per each location, all the forward/inverse modeling functions should still work. The easier for you is probably to fill the .Loc structure in the channel file with only one 3D position (make sure you keep the correct matrix orientation: [3x1]).
You should adjust accordingly the Orient field (the normal to the sensor plane) and the Weight field (you can set it to [1], or leave it empty [], I think both options should work).
Francois