Reynolds number
When the speed doubles, the Reynolds number also doubles and that is what causes the flow to detach. That is why fast cars need a more sloped shape than slow cars to have attached flow. And why the VW Beetle may have perfectly attached flow at, just for example, 20 mph, but does terribly on the highway.
That comparison picture I made shows the two different shapes with the exact same condition settings.
The major difference at the front is that the extreme wedge shape has almost NO STAGNATION. 100% of the air is scooped over the top and sides, leaving flow underneath completely unmolested. Well, since that is 2D, it is all scooped over the top. The effect is the same for 3D, just integrate to get the effect of a bunch of thin slices stacked together.