Right. It depends on the wavelength. That's all I was saying. The shorter the wavelength, the more likely it is to reflect or absorb.
But it also depends on the material. Conductive surfaces tend to reflect all EM. For example, the metal sides of a microwave oven or the walls in an elevator block EM radiation no matter what the frequency.
But for non-metals, it depends a lot more on the frequency and on the material.