This is something I can't replicate, it just seems to happen randomly. Sometimes, when I'm close to an ally, who is on groundlevel like me, and try to use Guardian Angel on them, I don't fly to them, but instead get flung high up into the air. Last time, the height I reached was enough to reach the upper floor on the first point of King's Row - made for a pretty good escape.
How does this work? What do I need to do to be able to do that consistently?