Thanks for the clarification. I'm sure there are others among the PPRUNE community that can provide a more learned response than I, but I will offer a couple observations that may help motivate the conversation:
1. For sub-sonic wings, leading edge slat extension has very little impact on the slope of the Cl-Alpha or the lift generated at a particular AOA below that for stall. The main impact of leading edge slats is that their extension helps the flow stay attached to higher angles-of-attack. This pushes the stall AOA to higher values and similarly allows a given airplane to fly at slower speeds prior to stall.
2. Trailing edge flap extension increases effective wing camber and also causes an effective rotation of the wing in the trailing edge down / leading edge up direction. Both effects provide an increase in Cl at a given AOA. This is important when considering pitch attitude at low speed flight, particularly during approach, flare, and landing. With a clean wing (leading and trailing edge devices retracted) zero lift occurs at/near zero AOA. With trailing edge flaps extended, the zero lift point moves to a negative AOA, in some cases below -5 degrees. This allows generation of significant lift at low speed at pitch attitudes that are appropriate for approach/landing without undue risk of tail strike.
Hope this helps,
FCEng84