haldex clutch

Hi for the introduction I would like to explain what I know and what I am asking.

We have different kind of for wheel drive systems based on four kind of center differential:
the TORSEN(TM) differential,
the HALDEX(TM) clutch,
VISCO clutch or
simplest PLANETARY differential

thera are also different kind of combination, like we may have front and rear planetary diff with torsen center diff with predesigned torque ration (normaly 40/60).

We may also have center and rear torsen or even all three torsen, some systems also include 100% locking diff and reductor (TOYOTA landcruizer, VW touareg).

then simpler systems include haldex clutch (like BMW Xdrive, VW golf 4motion....).

According to VAG's transverse engine mount (golf/bora/new passat/leon...) haldex clutch is normaly disengaged so you have FWD, but when the haldex controller sense wheel slepage it engage the haldex clutch.

now here is my question;
according to BMW Xdrive, this is AWD with 40/60 torque distribution.

So how can haldex clutch act like torsen and distribute torque in 40/60 ratio for normal driving conditions (hard dry surfaces like asphalt), when there will be between 100/0 to 0/100 torque distribution when you have stiff connection of two shafts?
100/0 will be when front tires will be on asphalt, and rear on ice, and 0/100 will be when front tires will be on ice and rear will be on asphalt. 50/50 will be when all wheels will be on dry asphalt.

because if you want 40/60 distribution haldex clutch must slip in such a way that rear shaft torque is in ratio 6/4 with front shaft - but that mean material wear and lose of power.

I am going to guess marketing....
I think your power distribution is probably going to be governed by whatever style traction control system is on the vehicle, and probably controlled closely enough they can say a ratio without being sued....