Why, even with a strong wind behind the rock, we observe calmness and the absence of wave movement

Why, even with a strong wind behind the rock, we observe calmness and the absence of wave movement, but we do not see this phenomenon behind the reeds?

Even with a strong wind behind the rock, we observe a calm and absence of wave motion due to a physical phenomenon called diffraction. Diffraction is a wave bending around an obstacle. The phenomenon of diffraction is possible only when the size of the obstacle is comparable to the wavelength. The size of the rock is much larger than the length of the wave movement of air, and the size of the reed is much smaller than the length of the wave movement of air. Therefore, we observe calm behind the rock, but not behind the reeds.