I think (by the look of the videos I've seen) that shadows were rendered with subtractive blending in the PSX version. And I recall reading somewhere subtractive blending was broken on the PC port. It looks way smoother than the PC version, which seems to have a uniform color blended 50% with the background. If it was possible to at least toy with the individual alpha values of the vertices I think it would be possible to make them look much better.