Why isn't the sautille articulation affected by velocity?

R2Etude

I'm currently using the Amati viola with the sautille articulation, and I wanted to control the dynamics using velocity instead of the mod wheel. I have it switched to velocity just like I do for spiccato (which works fine), but it's not reacting to changes in velocity. Even with it switched to velocity, it still only reacts to changes from the mod wheel. I find it hard to believe a product like this would be THAT inconsistent in it's usage, so I assume I'm doing something wrong?