Ive only used JD2 benders, mine do not have to be fully closed to load the tube, but with the hydro they so sit all the way back. When tube is loaded and the slack removed, the ram extends about 1 - 1.5 inches. Ive read/heard that fully parallel arms create un-needed forces on the pins/bolts/frame also depending on the angle of the ram as mounted to the bender.
My arms sit against the frame arms (yours have gaps) i also made spacers to center the dies and followers in the arms.
Looking forward to your build