When my tandem was ordered, the frame size and stem size were chosen based on what my road bike currently was. When the tandem arrived, I noticed that the stem had been set in the positive rise position and that even with the stem flipped over, I was still about one spacer higher. I flipped the stem and put one spacer above it. The first long ride on the bike, I quickly noticed that the bar dropped at an angle slightly, meaning when I was on the hoods I was actually about one 5mm spacer lower than the actual measurement from the center of the stem, so I moved the spacer back below the stem.
I rode the tandem a few more times with this configuration and eventually came to the conclusion that I should run the stem up instead, so it's back to how it originally came. I wouldn't be surprised if you found that most people you questioned had at least a slightly higher stem rise on their tandem then they do on their single bike.
One thing you might want to consider trying on your single, possibly the next time you tape your bars is to have the levers moved up higher on the bar and the bar rotated down so the bottom of the drop is a little bit closer to level. This will make it easier to use the drop but will still give you a comfortable position on the hoods. If you look at the way your tandem is set up, you'll see that it has been fit this way, although I tend to set the bar even closer to level. The added bonus is it also gives you better reach on the brakes while in the drops.