they won’t move in unison because of the fluid drag in the cross pipe, so one will hit the rim before the other always. WHy do you want to reduce the travel? Do you mean the distance from pad to rim when they’re off i.e. how far the pad travels to hit the rim?
I don’t think mine move by 4x as much, but they do move at slightly different times on the lever pull.
I do have them set quite far out though - personally I find that better with the mount I’m using (KH brake mount), cos I like having the lever right up close to the saddle handle when I am braking.
I’ve got Magura rim brakes on my tandem (actually HS66, but the calipers are the same as HS33) and I wouldn’t say the pads move different amounts. The one on the lever side usually hits the rim first, like Dave mentioned, but when the brake is released they both retract equally. Perhaps your calipers are a bit sticky. My tandem is only ridden on the road so they’re not subjected to as much crud as they might be on a muni or something.
The pistons should come out at a fairly same distance. Try cleaning out the the pistons by pulling the brake lever & use warm water/soap and put a dab of Triflow or equivalent thin lube. If the problem does not go away, you want to re-bleed the brake line.