it does indeed taper and get bigger on the top and it's VERY NOTICEABLE! Especailly on a red, white, silver car with a black interior. I looked at the other mercede models while I was at the dealer and all the cars have some sort of gap although not as big but the biggest difference is they have a panel that covers up the paint so you never notice it. See the pictures below.
First pic is a CLA door. Notice the bare metal and paint showing where the door closes. This is what is seen when you close the door with the gap.
Now look at the following pic from a C-class. See how the plastic trim extends all the way to the end of the door? My Honda accord has this piece although it only extends about half way.
This pic is from a E-class. It also has the fake mb tex that extends to the end of the door panel otherwise there is also a gap although not as big
With that said I believe I can fix it and do it pretty tastefully by using some fake leather vinyl and creating a panel similar to the ones from the other models. I have some experience working with leather and installing leather seats and I can do it professionally. If I end up purchasing this car I will definitely do this mod. I may make a kit for people on this forum. Just depends if i decide to go ahead purchase this car or not.