The amount of pitchbend in cents/tones/semitones is determined by how the VST interprets the midi information sent by the midi controller. Pitchbend values range from 0 (pitch fully bent down) to 16,383 (pitch fully bent up) where 8,192 is no bend (central position). So if a VST is only bending e.g. ±1 semitone, you are never going to be able to change anything at the controller end to make it bend ±2, you can only do that by adjusting the pitch bend settings in the VST.