Auto Leveling Z homing position and extruder distance?

I just upgraded my Prusa i3 to have auto leveling, and although everything works fine when homing the Z axis it probes outside of my bed, rather then on the build plate (causing a crash). What firmware setting do I change to fix this?
In addition, when following Tom's guide (https://www.youtube.com/watch?v=EcGFLwj0pnA) he says to send G92Z10, to calibrate the extruder height - however this does not work for me. How do I do this?
Thanks in advance.

Edited 1 time(s). Last edit at 01/31/2017 11:46PM by mcm001.

You should be using:
// Use "Z Safe Homing" to avoid homing with a Z probe outside the bed area.
//
// With this feature enabled:
//
// - Allow Z homing only after X and Y homing AND stepper drivers still enabled.
// - If stepper drivers time out, it will need X and Y homing again before Z homing.
// - Position the Z probe in a defined XY point before Z Homing when homing all axes (G28).
// - Prevent Z homing when the Z probe is outside bed area.
#define Z_SAFE_HOMING

#if ENABLED(Z_SAFE_HOMING)
#define Z_SAFE_HOMING_X_POINT (((X_MIN_POS + X_MAX_POS) / 2)+7) // X point for Z homing when homing all axis (G28).
#define Z_SAFE_HOMING_Y_POINT (((Y_MIN_POS + Y_MAX_POS) / 2)+12) // Y point for Z homing when homing all axis (G28).
#endif

And... You should not be using G92. If you need to adjust the Z_OFFSET_FROM_EXTRUDER you should either be changing it in Configuration.h or using the M851 command.