Many helicopters with dual controls are limited to being flown from the right seat single-pilot because...... well, just because. The controls, switches, and knobs that may require manipulation sometimes can only be reached from the right seat, because the manufacturer put them there. The right seat has become traditional for various reasons, some of which make sense. If you're in the left seat, and you need to tune a radio, do something with the GPS, or do anything else with switches, controls, etc, then you have to change your hands so that you control the cyclic with your left hand while you do what needs doing with your right hand. If an emergency, such as an engine failure occurs while you're doing this, then you have to do a lot of switching to take care of it, and in some models a second can become a lifetime. From the right seat, it's a relatively simple matter to just hit the collective with the left hand and go into autorotation, with little loss of time.
The story goes that the first Sikorsky(??) model with two pilot seats had only one collective, in the middle, and flying from the right was preferable to the pilots, who were right-handed. I won't swear to the truth of that, though, because I wasn't there.