Softening the corners

Cinched Plastic Bottle 001.3dm (428.3 KB)
Can anyone help me arrive at a more accurate solution to these corners marked. I am trying to copy a bottle and am stumped as to how they got the corners so smooth. I also need to shell the object to 1.5 mm without a lot of cleanup work. This example can do that but the corners are terrible. I’ll upload a picture of the sample soon


Here’s a picture of the sample with softer corners

The arched surface has corners that are deeper than the four sides.