Hi,
I would think that part of the reason that contrast is higher, when looking from an angle is simply that "printed area dot density" increases, while in "unprinted" areas there are "no dots" that could look denser from an angle. The smooth surface and the slight gloss of the screen might increase the effect.
With printed samples similar effect can be seen. Try it your self or look at the enclosed picture. With the e-ink structure the effect might be stronger as the colour particals actually form a "3D dot" bellow the screen surface, instead of the 2D print surface. From sideview you might see the surface and a hint of the dot depth?
