I think the best idea is to put as little stress on the seam as possible - outside = tensile stress ; inside = compressive stress.
The best place for the seam is close to perpendicular to the bend. Rotate the tube so the seam is about 10 degrees towards the inside of the bend from the bend axis. This area experiences the least ammount of compressing or expanding.
The best place for the weld is up or down. This is 1/4 turn from the dies. IE not faceing or away. This puts less stress on the weld. The lower stress on the weld the better. The weld is the harder material in welded tube or pipe and gets the least ammount of tension or compression when at the side of the bend. This info comes from years as an ironworker, and now the biotech industry. Miles and miles of bent tube and pipe.
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