Basically, you're talking about horizontal tail volume. Dutch roll is seldom a problem with our models. But pitch sensitivity is.

The reason model's tails were enlarged years ago was because years ago the RC equipment wasn't very good. And a lot of the models were free flight designs originally. They needed the "extra" stability back then.

Nowadays we get by with less stable models. Our radio equipment helps us do that.

If you're laying out a scale model that you're going to compete with, it's important to try and keep the scale outlines. It can bite you, however. You can wind up with a really hard to fly model. But if you're not drawing up a pure scale model, what's the problem? Fudge the fuselage length a bit. Fudge the aspect ratio of the horizontal tail some, and make the chord a bit longer. Keep the proportions of the horizontal tail and nobody will notice.

Heck, almost all the "scale" arfs nowadays have flat surfaces anyway. Just depends on what bothers you and what doesn't, and what you can actually see and what you can't.