DB is correct about the travel, I have four Scott releases and the tension screw is only for the travel adjustment. This actually increases or decreases the sensitivity of the trigger pull. If you adjust it to the point beyond the roller staying in contect the jaws will not stay closed. I have all of mine adjusted just before this point, so I don't have to feel like I am yanking the trigger to get it to go off.
The trigger pull being very light when not attached to the string, is only because the jaws do not have pressure applied to them. This is turn allows the jaws to open more freely, these are designed to apply counter pressure to the roller when attached to the string. Hence, you've got tighter trigger pull when at full draw.