Why can reflections from the ionosphere make radio direction-finder bearings less accurate?

Reflections from the ionosphere can significantly decrease the accuracy of radio direction-finder bearings because they alter the intended path of the radio waves.1

Under ideal conditions, a direction finder can typically provide bearings within 1° or 2° of the true value. However, because radio wave propagation is highly variable and subject to changes in the ionosphere, the incoming signal may not arrive directly from the transmitter. When waves are reflected or refracted by the ionosphere, the direction of arrival is shifted, leading to errors in the bearing. This phenomenon is often associated with the "night effect," a shifting of the apparent direction of a signal that is most commonly observed at night when ionospheric conditions change.123