Pitch Bend flat region

The range (y axis) of the pitch bending graph on the right goes from 0 to higher frequency region. In other words, this can only produce pitch bends that go upwards.

If I want to introduce a pitch bend that starts from a lower note and goes upwards, I'd have to write in the lower note to the sheet music and guess how high pitch bend goes which seems counter intuitive as I'd like the musician the to read the note to end on, but start on an arbitrary flatter sound (by a few semitones). This doesn't allow bending from the flat side of the note.