Is the OP saying that he could ride singles off his wheel on the flat if only he had bigger gears? I've ridden my single behind some strong tandem teams, including 2 captain with a strong stoker. It's pretty hard to do. I he's talking about during descents, very shallow descents where one can gain speed by pedaling beyond 40 are rare. I've never seen one, though I understand they do exist, like on the east slopes of the Rockies. Most descents, when we hit about 35 we're faster if we stop pedaling and tuck, pedals level, knees in, flat back, chin on stem, elbows under diaphragm, stoker's head on my butt. We're gone. If there's a single that knew to be abreast of us as we went over the top, a quick swerve left and they're gone, though we usually don't do that.
The problem with trying to drop people on the flat is that power required for the lead bike goes up as the cube of the speed. So when you hit the climb, you're already cooked. Smarter to let them pass you on the climb, then sprint over the top and crush them on the descent. They can't get on because you're going 10 mph faster than they are. Then you never have to ride them off your wheel. You'll each be putting out less average power than they will on the flat, heading for the next climb. This is all, needless to say, dangerous, which is why people don't recommend racing tandems against singles, unless the singles know the routine and will stay the heck right.