The title might be a bit confusing. Let me try to explain.
When I switch on velocity x-fading (for violins, say) then the sound is generally much louder than with velocity x-fade switched off, even if the controller value matches the note-on velocity.
To make it even more explicit: Map the "vel xf" fader to "note on velocity". Now it should make no difference if the "velocity x-fade" button is switched on or off, right? But it does. What's this?