Increasing the dwell does not directly reduce pressure, however it allows you to make other changes to do so.
Dwell is the setting for how long the ram holds the hammer forward, thus keeping the valve open and gas flowing - for a high dwell setting, the valve is held open longer.
Closely associated with Dwell in the operation of the Angel is the LPR pressure. Basically this controls how fast and hard the ram moves the hammer. As the LPR pressure drops, the valve is opened less, reducing the amount of gas that will flow before the ram withdraws and the valve closes.
The idea is that as you increase dwell, you need to reduce LPR pressure, and vice versa. With high dwell/low LPR you are meant to put less impact on the ball and thus can use more brittle paint, at the expense of gas efficiecny.
For a dwell of 17, try removing 2-3 shims, thus reducing the LPR pressure of your LCD by approx. 7 to 10 psi.