I have no clue what iib is trying to say, so I'll work with this.
The above doesn't make much sense. The BD hanger is somewhat free-floating, so no matter if the screw is placed at +5 or -5 degrees (or more?) to horizontal, the hangar will point straight down. As long as the force is applied straight down, it doesn't matter how long the hangar is, since there is no moment arm.
Now, let's imagine that the BD hangar is 3 inches long, and is fixed relative to the screw, at 90 degrees. Now, when you place said screw at 90 degrees to vertical, the load on the hangar is at 90 degrees to the screw, and the hangar can exert no torque. So, in this case, the screw will have the same pull out strength no matter where the biner is clipped (momement is zero). No, if we tilted the screw at +5 degrees (ie, hangar is higher than the teeth), then the hangar will indeed exert a torque on the screw, increasing the loading of the screw near the surface of the ice.
Now imagine that we take this hypothetical screw, and place it at -5 degrees (ie, teeth higher than hangar). Now, with the aforementioned rigidly connected hangar, the force will create a moment around the screw that actually pivots around the teeth of the screw, decreasing the load on the ice near the surface, at least below the screw (the screw will try to pivot around the ice above the screw).
But this is useless speculation, since the free-floating hangar design of the BD makes the hangar exert no moment whatsoever within the range of normal placements. So, the hangar design differences between Grivel and BD have no effect upon screw strength.
So, I conclude that
a) IIB is drunk, crazy, or stupid
or
b) he didn't mean what JayB is talking about. In this case, I humbly beg elucidation of the subject at hand.
Geek in training, over and out.