Altering exposure and development will usually be most affective of the overall density range of the negative. Thus the high and low values are determiners of the mid tone separation consistant with the curve of the particular film
In order to arrive at better midtone separation, it is normally necessary to overdevelop to an extent and then to deal with the excess density range at the printing stage. This can be handled in printing in several ways. Among those are contrast reduction masking of the negative (brings the shadow densities upward), flashing the paper (brings the highlight densities effective downward), or one can make a specific shadow through midtone contrast enhancing mask (specifically increases constrast in a portion of the density range). The latter requires pin registration capability.