It is exactley the same for DC3, C172, Tiger moths and gliders- nothing to do with modern aerofoils.
I didnt say that, but since you brought it up, modern airliners use
supercritical airfoils which usually have a "flatter" bottom drag bucket.
They also have a higher L/D ratio for the same Cl than conventional "old" airfoils
so I wouldn't say "exactley the same".. .
XPM