These I take to be normal features of any good tonal progression. I differs from the previous one only in the position of the substituted progression. The reason why the phrases include at least one substituted progression is that this is the necessary condition for the phrase to return to its starting point, the tonic. A continued series of unsubstituted dominant progressions, following a cycle of fifths, indeed, could only inexorably lead away from the original tonic. A well formed tonal phrase can therefore be defined, from the point of view of harmonic progressions, as a series of dominant progressions of which at least one is substituted.
Dominant progressions appear as lines descending from left to right.
The overall Z shape of these figures, which I take to be characteristic of a well formed tonal phrase, differs only in the position of the dotted lines. Although it may be difficult to obtain statistics for the tonal corpus as a whole, I consider these figures to be quite typical of the common tonal practice. Subdominant progressions in some cases may be more frequent, but they are normally not found in immediate succession, unless for special effect. The repetition of the motive in mm. 37-39 is tonally more affirmative, in part because it is constructed on dominant progressions.