I believe S speed indicates the lowest speed in config 1, Minimum speed with slats out. Below this speed you should have Flap 2 selected. Flying near VLS is dodgy and as has been noted before, on an intercept where the aircraft can command upto 30 degrees of bank to pick up the LOC, you could end up with egg on your face as the aircraft goes into Alpha Floor! If you fly 321 you will definitely need flap 2 at 180 knots as S speed tends to be around 200 knots, I have seen a number of pilots make this mistake.
