Yep! the reason why your offsets are different values on the heavy fighter wing components is because the top peace is only moved in the Y direction and the lower wings are moved in the X as well as the Y.
So for instance the wings need to be at a radius of 3 units offset from the attach point of the parent piece. The top piece only needs to move in the Y direction 3 units, since the piece(s) attached axis will have the same axis as the attach points normal axis and that match's the direction you want to offset it.
The lower pieces need some X movement as well as Y, so to get to the radius of 3 units(h) at an angle of 45 deg (A) for example, then distance X and Y (a) = CosA x h = a.
So: Cos45 x 3 = 2.12 (rounded)
X and Y need to move 2.12(rounded off) units to get to a radial distance of 3 the same distance as the top piece has move only in Y.
Well, sorry if I didn't explain that too well. I guess the thing to remember is that any piece attached, will inherit its axis from the normal of the attach point and not have its own local axis.
It would be a nice addition to the ship designer if we could toggle to local space of selected pieces for translation (offset), like it does for rotation and scale. Maybe since rotation and scale do go to local space, perhaps the offset is supposed to as well and it could be a bug.
Great work as always Gauntlet03