I'm not understanding bed coordinates.

I built a printer using RAMPS 1.4, Arduino 2560.
IR sensor
Firmware: Marlin RC-6.

I'm having a problem understand the coordinates.
Using Repeiter Host, if I home the X and Y axis, the hot end moves to the X=0, Y=0 as you would expect. But if I try and home Z at X=0, Y=0 I get a "Z Probe Out message". The nearest that I can do a Z home is X=30, Y=10.

Marlin Settings:
#define X_MAX_POS 170
#define Y_MAX_POS 260
#define Z_MAX_POS 200

#define AUTO_BED_LEVELING_GRID

#if ENABLED(AUTO_BED_LEVELING_GRID)



#define LEFT_PROBE_BED_POSITION 30
#define RIGHT_PROBE_BED_POSITION 140
#define FRONT_PROBE_BED_POSITION 50
#define BACK_PROBE_BED_POSITION 250

#define MIN_PROBE_EDGE 10 // The Z probe minimum square sides can be no smaller than this.

// Set the number of grid points per dimension.
// You probably don't need more than 3 (squared=9).
#define AUTO_BED_LEVELING_GRID_POINTS 3

#define X_PROBE_OFFSET_FROM_EXTRUDER -30 // X offset: -left +right [of the nozzle]
#define Y_PROBE_OFFSET_FROM_EXTRUDER -8 // Y offset: -front +behind [the nozzle]
#define Z_PROBE_OFFSET_FROM_EXTRUDER .95 // Z offset: -below +above [the nozzle]

Your help would be appreciated.