Additional measurement points placed beyond the accessory's outer edge to capture how the magnetic field falls off into open space. Improves heatmap quality at the boundaries and shows where the useful field actually ends rather than where the coil ends. Default: 1 extra point for discs and loops, 0 for rectangular mats. Spacing of these points anchors from the accessory edge, not from the last interior measurement.
The field is measured on a grid. Starting at the center, the test engineer steps a probe outward along each axis at a fixed point spacing, taking a reading at every point, and continues a little past the accessory edge to catch the field as it fades. The origin is the center of the accessory surface.
