Re: UBL - how are probe points calculated?

Further to my first post, I decided to simplify the issue and give some more details
Notice that even though a 3*3 mesh was called for, only 4 positions were probed. The high X and Y positions show as unreachable.

Any comment on why the high points are unreachable and/or how the probe locations are determined would be appreciated


#define X_PROBE_OFFSET_FROM_EXTRUDER -40
#define Y_PROBE_OFFSET_FROM_EXTRUDER -9
#define X_BED_SIZE 319
#define Y_BED_SIZE 300
#define X_MIN_POS 0
#define Y_MIN_POS 0
#define Z_MIN_POS 0
#define X_MAX_POS X_BED_SIZE
#define Y_MAX_POS Y_BED_SIZE
#define Z_MAX_POS 400
#define MESH_MIN_X MESH_INSET
#define MESH_MIN_Y MESH_INSET
#define MESH_MAX_X X_BED_SIZE
#define MESH_MAX_Y Y_BED_SIZE
#define GRID_MAX_POINTS_X 3
#define GRID_MAX_POINTS_Y GRID_MAX_POINTS_X

Commands sent via command line in octoprint:

G28
g29 p1 g29 s1 g29 a m500

x/y coordinates visited as per LCD display

202/162
202/14
45/162
45/14

The high X and Y positions show as unreachable in the bed mesh
The minimum X and Y positions are obviously chosen so that combining the probe offset from the extruder location yields a probe point that falls at the mesh inset point (ie when the extruder is at 45/14 and the x/y mesh offset is 5/5 the probe is at 5/5 which is the first possible position it is allowed to be)