Now seriously confused!
Low'n'slow - You mentioned the 737 having vortex generators UNDER the leading edge of the wing but still attached to the slat. I know that there is two groups of generators on the upper surface just o/b of the pylon, and then further out towards the tip, but have never seen them below the wing - is this on a 737NG?
I have also noticed the 4 on either side of the rear fuselage and just assumed that they are there to improve the airflow over the lower section of the rudder as ther is quite a gap at the bottom where it sits on its seal. But I could be wrong (wife tells me I usually am!!) and if anyone can enlighten me - great!