A new mixed tandem team rode with our group for a while. She (stoker) was a much better and more experienced rider than he. It seemed to us that he felt pressured to perform and consequently couldn't relax and enjoy the ride. He was actually a terrible captain. Too strong minded to allow himself to, I don't know, meld with the world. They quit riding with the group, which we appreciated after they had a few close calls.

That's probably not you, but is an illustration of how difficult captaining can be mentally. One thing I (captain) did after we got our tandem was to almost completely quit riding my singles. We both only rode the tandem and that's still the case after 9 years of tandeming. Singles and tandems do handle very differently. Now when I get on a single, that thing is all over the road for the first 5 miles. Only riding tandem hardened all my reflexes into appropriate tandem reflexes. We think nothing of riding that bike in city traffic or difficult terrain.

One realization that helped me to relax is the idea that with a single the rider has pretty much complete control over every tiniest motion of that bike. On a tandem, no matter how excellent the stoker, that isn't true. So I think of the direction of our forward motion as a vector. As long as all the minor motions the tandem makes add up to that same vector, it's all good. In other words, as long as the bike keeps heading in the general direction that I want, the little stuff doesn't matter. It's no good trying to make small corrections for every little deviation from the course I want. Better to just relax.

Another poster mentioned bar width. I run 40cm (c-c) bars on my singles and 44cm on the tandem. That works very well.