I'm not sure you can draw meaningful conclusions from a test figure with so few polygons - but I think you're probably right. I forgot to point this out earlier, but if you look at the first two pictures in my test thread, linked above, it seems to me that the lower square (which is the parent) retains its edge vertices in the same position, whereas the child square becomes more distorted as the weld distance is increased. This would bear out your theory that the parent has priority, as it were.

Quote - what i found most odd is that making the parent actor invisible breaks the weld

I was surprised but not astonished. I already had an idea there are some areas where making geometry invisible removes its influence; and others where it doesn't. If I think about it I may be able to come up with a list, but it's late here. :)