Augmentation dots should follow stem direction, not voice number.
The top bar of the attached shows what I understand to be the proper placement of the augmentation dot on the note on a line. The dot is placed in the space above the line because the stem is down. This uses voice 1.
The lower bar uses 2 voices with the 2 voice below.
As one can see there is a different placement of the dot. The top bar showing the dot placed in the space above, the bottom showing the dot in the space below. Both stems are down.
If one changes the stem direction in any voice the dot stays in that position.
So, I suggest the dot should be ties to stem direction.
If the stem direction doesn't matter, then why is the dot no constant in all circumstances? :)