After adding Subsurf modifier, some UV is distorted As title said, after adding Subsurf modifier, some UV is disorted.

If mesh has simple geometry, I can fix it, but sometimes it's too complicated or can't fix it because it's getting worse.

This is the example model that I faced this problem:



Top image is low poly and lower image is high poly mesh that applied sub-surf modifier.

As you can see those red lined boxes, some UV is disorted and I can't fix it.

Is there a way to fix this problem?

Also I mostly prefer using Smart UV Project, because when I unwrap my mesh manually, each UV island has different ratio.

Is there a way to adjust ratio of UV islands automatically?
Using subsurface modifier will not 100% guarantee that has perfect uv result. I already told in comment, however if you want to add more geometry after finish modeling, should be careful to not messing up the UV to watch carefully while adding additional geometry.

This especially messing up that adding more edges in curved geometry, so it's just better to remap your UV to new Geometry.

If you using Substance Painter for creating texture, don't be afraid, the program will automatically repaint all your previous works even the geometry and UV's are changed(but not 100%).