In our RC Gliders size DOES matter. To lead off the long list of advantages they have more efficiency due to the larger Reynolds number range they fly in. If this doesn't mean much it's basically the measure of how efficiently the air deals with our models. Larger "fits" the passing air better and so the wings perform better in every way.
Now add to this the higher launches because the weight and drag of the line is not as large a percentage of the model. The fact that you can range out farther before you hit your limit of visual perspective and you've got some pretty good reasons.
This isn't a small advantage either. There's a noticable difference going from 2 meter to 100 Standard class and up to open class. Even there you can see the difference between the 110 to 120 inch and the 130 to 140 inch open designs.
I'd say from what I've seen that it's safe to say there's about a 25% to 30% advantage between a 2 meter and a 110 to 120 inch open class design in terms of flight times flying in marginal air where the models have to struggle to stay up but don't quite make it...... I had to set the conditions that way because if there's decent thermals then they are all good....
