Cast shadows (as opposed to drop shadows), on the other hand, would appear skewed since they appear ON the surface.

One way to improve the effect would be to apply Blur to the reflection, but it would be best to have a gradient or ramp applied to the Blur Radius, if that’s possible. It should NOT be blurred much “close to the surface” where it’s bright, but should be blurred more as it gets further “into / under the surface” where it’s dimmer. This simulates the dispersion effect of the imperfectly smooth reflecting surface.

I’m still new to Expression, so I don’t know if that’s possible (applying ramps to Blur Radius) short of making a custom Effect, but I do know how 3D modeling / rendering works, and for truly realistic reflections, that’s what’s needed.