Question:How does Diffraction change with different obstacles or gaps?
As the size of the gap gets closer to the wavelength of the wave the amount of diffraction increases.
Maximum diffraction occurs when the wavelength of the wave is equal to the size of the gap.
For obstacles (instead of gaps) diffraction around the obstacle increase as the wavelength of the waves increase.
Radio waves have much longer wavelength than microwaves; so radiowaves diffract much more round any given obstacle - such as mountains and buildings.