{X,Y,Z}_{MIN,MAX}_POS are actually in Gcode coordinates.

Marlin/Configuration.h

 #define Y_HOME_DIR 1
 #define Z_HOME_DIR 1
 
-#define min_software_endstops false //If true, axis won't move to coordinates less than HOME_POS.
-#define max_software_endstops false //If true, axis won't move to coordinates greater than the defined lengths below.
-
-// Travel limits after homing
-// For deltabots, the MAX_POS doesn't have to be exact, it will be recalculated from MANUAL_Z_HOME_POS below.
-#define X_MAX_POS 620
-#define X_MIN_POS 0
-#define Y_MAX_POS 620
-#define Y_MIN_POS 0
-#define Z_MAX_POS 620
+#define min_software_endstops true //If true, axis won't move to coordinates less than *_MIN_POS.
+#define max_software_endstops true //If true, axis won't move to coordinates greater than *_MAX_POS.
+
+#define X_MAX_POS 90
+#define X_MIN_POS -90
+#define Y_MAX_POS 90
+#define Y_MIN_POS -90
+#define Z_MAX_POS MANUAL_Z_HOME_POS
 #define Z_MIN_POS 0
 
 #define X_MAX_LENGTH (X_MAX_POS - X_MIN_POS)

Marlin/Marlin_main.cpp

       0) {
     current_position[axis] = 0;
     plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
-    destination[axis] = 1.5 * max_length(axis) * home_dir(axis);
+    destination[axis] = 3 * Z_MAX_LENGTH;
     feedrate = homing_feedrate[axis];
     plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate/60, active_extruder);
     st_synchronize();
         current_position[Z_AXIS] = 0;
         plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]); 
 
-        destination[X_AXIS] = 1.5 * X_MAX_LENGTH * X_HOME_DIR;
-        destination[Y_AXIS] = 1.5 * Y_MAX_LENGTH * Y_HOME_DIR;
-        destination[Z_AXIS] = 1.5 * Z_MAX_LENGTH * Z_HOME_DIR;
+        destination[X_AXIS] = 3 * Z_MAX_LENGTH;
+        destination[Y_AXIS] = 3 * Z_MAX_LENGTH;
+        destination[Z_AXIS] = 3 * Z_MAX_LENGTH;
         feedrate = 1.732 * homing_feedrate[X_AXIS];
         plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate/60, active_extruder);
         st_synchronize();