Originally Posted by B. Carfree

There's no real basis for it as long as the larger rider is competent to ride as stoker. This seems to be such a problem that the default set up is larger male as captain and smaller female as stoker. By competent to ride as stoker, I'm referring to being able to generate power without shifting the bike from side to side or fore/aft. Sadly, this has become a vanishing skill over the years (I blame power meters. Prior to their advent, cyclists were taught to ride "quietly" for best power; the meters put the lie to that.)

My wife and I have been riding large male stoker/small female captain for twenty-five years. The advantages are many:
1. Both of us can see down the road. Since we ride in areas with lots of wildlife, this has been critical for safety many times.
2. We can set up the bike so that the stoker controls the shifting. Since I can see the road ahead, I can do the shifting. This not only takes a load off the captain, it allows for shorter cables which results in better shifting performance and easier procurement of replacement cables if one should break while on a tour. We just happened to have such a cable failure on a tour last Spring and it was nice to be able to roll into the nearest bike shop and get a replacement. This also allows us to use cheaper shifters.
3. Stoker can control the drag brake. Again, this allows the captain to have an easier time. On long descents, she just steers and watches for road defects and wildlife.
4. Okay, everyone misses a clip-in once in a while. When it happens to us, it's the stoker who is looking down to correct. When it happens to those who have the larger person as captain, he's both handling the steering and looking down to get back in. I think our set-up works better in such rare situations. We did have one miscommunication at a stop sign where I was certain we were going to roll it at 3 mph and she was just as certain we were going to come to a complete stop. I was pleasantly surprised that I could unclip both feet and land on my side without taking the bike down. (Never allow the smaller rider to hit the ground is a good rule no matter where she is riding.)
5. We get a lot of positive feedback from motorists, even in this somewhat bike-hostile area.
6. It's nice to be able to ride myself into the ground knowing that if I get totally beaten my captain can still safely guide us home. If I was riding captain, I'd have to keep something back just for safety.

The main downside is that we can't ride an off-the-shelf tandem. This hasn't been an issue since custom rides aren't very expensive and we started out with a bike that was able to accommodate either orientation, albeit with a bit less reach than I would like. (I was younger and more flexible then.) There must be some other disadvantages, but we haven't noticed them. I suppose we will never be able to use a Gates belt since the distance from our cranks will always be too long, but I don't know if we would ever want to bother with one.