As far as I know the ESP has nothing to do with power transfer.
The Haldex controller does the power transfer based on throttle angle, speed and front wheel slip. I'm not sure if there is a 'normal' power transfer as it will vary constantly depending on conditions. At high speed with no front wheel slip I thought it was 100% fwd ( could be wrong though ! ).
The ESP has two parts really, traction control (ASR/EDL) and ESP itself. With the system on the ASR/EDL will brake any wheel that spins ( front or rear ) and can reduce engine power to stop wheel spin - with if off it won't intervene. With it off you could get all 4 wheels spinning on ice or very slippery roads as the hadlex will distribute the power to all 4.
The ESP part takes into account steering angle, yaw rate, and wheel speeds to stop the car from understeering or oversteering. So if you go into a corner to fast and start to understeer it brakes the inside rear wheel and can but power to bring the car back on line. It does this for oversteer to by braking the front wheels as needed.
As far as I can tell the ESP part is never completely disengaged - so with ESP off you get on ASR/EDL plus a later acting ESP. It lets the car slide more before intervening but will still intervene in extreme situations. I've never seen the light flash or felt intervention with the system off though - but I probably wasn't trying hard enough!
I'm sure I'll be corrected if my understanding is wrong!
