Hello and welcome.
As far as I understand the value range for any Note Expression parameter is governed by the VSTi, that you are sending it to. Unless it is a generic MIDI 1.0 message. Pitch Bend is using the usual -8192/+ 8191 for pitch bend (MIDI 14bit value range). I can see Retrologue doing that.The VSTi tells Cubase that its Tuning parameter works from -48 to +48 and it is programmed to work in semi-tone steps. Well, actually you can define the range in the key editor, as it is a VST3 parameter, not MIDI:
I haven’t found any way to snap the pitchbend to semitones in the editor.