The significance of reynolds number is that at the same reynolds number, the flow pattern over similar shapes will be similar. At a given viscosity and density, reynolds number is proportional to velocity times flow length (wing chord). As the reynolds number decreases the boundry layer thickens. the boundry layer is the layer over the surface where the flow is shearing (going from zero to the local flow velocity). At full scale reynolds numbers the rate at which the boundry layer thickens with decreasing reynolds number is much lower than at model reynolds numbers.

Because the boundry layer thickens at lower reynolds numbers the airfoil drag goes up as though the airfoil was thicker. Because there is less energy in the flow at lower speeds the flow transitions from laminar to turbulent sooner and from turbulent to detached sooner. At model speeds, laminar flow airfoils don't have enough laminar flow to be significantly lower drag than nonlaminar flow airfoils. Since seperation occurs sooner airfoils at low speeds can't achieve as high lift coefficients as the same airfoils at higher speeds.

Fortunately for aerobatic models low drag is not a high priority.