The problem here is that you are comparing a real life situation, with how we handle things in the engine. The information I shared came directly from one of our rendering guys who knows lighting and materials very well. I understand your points about SS in the real life, but what you are seeing as described to me is what is expected. As you are aware, the engine cannot simulate every real life lighting situation as that would be incredibly complex and not really easy to use for games. We use a number of different techniques and features to simulate and fake various effects to try and resemble phenomenons like SSS. This is the beauty of game design, it sometimes doesn’t work out of the box like you would expect, so you will need to find a way to work around the problem if it is that much of an issue, which I am sure you can figure out 
Thank you,