The ratio of fixed to movable varies from 1:1 to as little as 5:1 depending on the sort of model. All of these work fine but the smaller ratio elevators require more deflection angle to achieve a desireable level of control. The smaller ratios are typically found on trainers and gliders.

More important than the amount of movable area is the surface area of the horizontal surface being large enough to properly stabilize the wing and putting the balance point at a position that is in harmony with the size of the horizontal stabilizer and the distance from the wing. You can test this for yourself using the online CG calculator links found in the resource thread at the top of this forum's thread listings.