I think the basic problem with trying to obtain more difuse illumination, is that the buttons are not shaped for it. Think of each button as a lens, bending light to its whim.

The top button is a convex lens, focussing the LED light straight forward -- practically invisible from the sides, but nice and difuse when viewed head-on.

The botton/left/right buttons are all concave on the surface, focussing light to a point at the centre of the button.

I like the current shapes, but one side-effect of them is that the light may never be as difuse as some would like it to be.

Cheers