I think my problem may be something different from that setting -- probably a more basic lack of knowledge about using controllers. Today I got myself really hosed up on that same project, with the MIDI running into Dimension. Everything was almost exactly the way I wanted it, but I wanted to put a decrecendo on the final French horn chord. As I was already working on the MIDI velocities, I figured I could do the decrecendo by adding a controller for "volume".
That actually worked, but proved to be far too tedious to get a smooth curve. I thought I would wipe out the volume values and just use fader automation on the WAV coming out of the synth. I deleted that whole volume controller in the MIDI window (while the velocities remained as usual.) As soon as I did that, the whole track went silent. And now I couldn't see any of that volume information. I had to create a new MIDI track and cut paste all the notes into that (without any volume information), and then it was fine again.
Obviously I made a wrong turn along the way.
Another related question. That original MIDI file that caused my Aria problem seemed to have 4 different controllers (velocity, sustain pedal, and a couple of others.) All I really wanted was velocities, and I needed to edit them to give it a more human feel. But with 4 controllers in the piano roll view, the velocity bars are about 4 pixels high, and cannot effectively be edited. I couldn't find any way to expand the velocity scale so I could edit that. How do you guys handle that?