Why are some riders so good to draft?

I don't know if I fully understand what makes one rider so easy to follow that it's like drafting a locomotive, steady and safe and luxurious. And another rider, equally strong and equally adept at bike handling, may be far more difficult to follow, so that he or she makes you uneasy and frustrated at the changes of pace.

We can't talk about speed here, because speed is relative to all sorts of conditions. We mean pace. We mean something like perceived level of effort. The good rider to follow keeps a consistent level of effort, and following that person is almost restful. It's deluxe.

The rider who appears to be steady and solid but whose pace rises and falls even just slightly will have you riding with your fingers on your brake levers and dropping back so you have a space, a cushion, against his or her slight changes of pace.

You can ride around the equator on one PowerBar and a half full bottle behind the first rider. You can hardly stand to ride a mile behind the second.

Maybe it's the gear chosen by the good leader. I think that a slightly higher gear smooths out the pace changes over slight rises and dips in the road, and perhaps pace changes from shifts in wind direction or velocity. Like riding on rough surfaces, a higher gear will lend itself to a steadier pace. Not a giant gear, a slightly higher gear. A tooth or two.

Maybe the good leader senses the effort that the drafting rider is exerting, and tries to make it steady, not spiky, not pedal-coast, pedal-coast. Maybe that leader understands the drafting dynamic on some level that he or she can't explain.

I have thought about it and can't come up with a solid oh-THAT's-why kinda answer. If you have ideas about this, about why one person is a delight to follow and another is a nightmare, please comment here on my blog page.