Hi Pozero, this can work in different ways depending on how your rendering software is set up.

My guess is that your program calculates smoothing by a sort of averaging process between adjacent polygons.

Probably when you exported from MoI, you had welding turned off - this means that the polygons are created in separate pieces for each surface, they are not connected into the same vertices where you see that line. The vertices may look like they are the same but they are just 2 vertices stacked up directly on top of one another, if you were to go in there and move the vertices around you would see that they are not connected and can be moved separately to open up a gap between the polygons.

Usually a polygon modeling program will have an operation called "weld" or "merge vertices" that can be used to remove those duplicate points and make those polygons share the same exact vertex - that makes then connected to one another and then smoothing should flow across them.

So try to find that "weld" or "merge" function and use that to eliminate that crease.

- Michael