
I noticed that they were not down the direct centre line of the aircraft, most offset to the left ( in the pictures) and the last offset to the right.

I always assumed they were on the centre line (as depicted on all model kit airliners I have built where supplied) but it obviously not the case. I assume the reason is that there is a structural member running the length of the fuselage and the antennas can't be secured there.
Is this also the case on other Boeing types and other manufacturers aircraft?