After a lot of screwing around, I have my answer!
I had MIN_PROBE_EDGE 5 set in configuration_h which would not allow a probe cycle at 0 or 300
The position for probing points is based on
(mesh_max - mesh_min)/ (# of probe points - 1)
For the result to be reachable it has to fall inside of mesh_max - mesh_min and it can not be in the min_probe_edge range
mesh_min and mesh_max reflect any configured mesh_inset parameters
I hope I got all that right in case anybody else gets confused about how the auto probing determins the points it uses
I had MIN_PROBE_EDGE 5 set in configuration_h which would not allow a probe cycle at 0 or 300
The position for probing points is based on
(mesh_max - mesh_min)/ (# of probe points - 1)
For the result to be reachable it has to fall inside of mesh_max - mesh_min and it can not be in the min_probe_edge range
mesh_min and mesh_max reflect any configured mesh_inset parameters
I hope I got all that right in case anybody else gets confused about how the auto probing determins the points it uses