Hi,
I imagine that they refer to the Trigger input, I see that it responds to different levels of the trigger, so the higher the peak voltage of the trigger, the greater the response of the internal VCA.
Other modules respond the same to a 6V trigger as to a 8V trigger or a 10V trigger. In this case, it appears that the trigger directly drives an internal VCA, so it is sensitive to the trigger voltage.
To take advantage of this you will need a sequential that has a velocity parameter or modulate the trigger before entering into the SY0.5.
Best regards,