Designs that are planned for simple flight can get away with the smaller size elevator. Unless you plan square eights or snap rolls, lots of quick force won't be needed. Perfect example is the Tiger. Try and get one to snap roll. I think the stock elevator is about 15% on the sucker. It's my understanding it was designed as a "enhanced" trainer. I had 3 of 'em and just getting the wing to stall wasn't something that tail could do easily.

Designs that are pointed at extremely efficient flight often have slightly larger than small elevators. Gliders are good examples. They don't need snap roll ability but want efficiency. They aren't going to get max efficiency from a short chord elevator that has to deflect a lot to get the job done. The less deflection, the better the efficiency.

You don't expect to need a lot of effect for "heavy work" like snaps and such, right. But want your slow flyer to stay in the air with minimal power? If those are your parameters, you won't need 40-50% elevators, but also don't want less than say 20%. I'm guessing.............

Say 30 sq.in for elevator and 100 sq.in for stab and you got a 23% elevator.