Are parallel v-brakes fixed distance? [Avid Arch Rival 50]
iirc - the Arch Rival V-brakes are described as parallel because the brake block surfaces are always parallel to the rim braking surface at whatever distance from the rim. This in theory improves braking.

Other than this - they function the same as a normal V-brake in that the arms act as levers to apply the brake blocks to the rim surface.

Adjustment may be a bit more picky - in that as the cable is loosened and the braking arms move outward - it will raise the brake blocks to keep them parallel to the rim. Therefore, to get the pads further from the rim - you may have to slacken of significantly more tension than with traditional V-brakes.
You may have to undo the cable entirely to slacken enough.