Complex sentence: The wing operates in the downwash from the canard surface, which reduces its efficiency although the effects of the downwash don't cause as large a problem as the tailplane would experience in a conventional set-up.
Split into simpler sentences: The wing operates in the downwash from the canard surface, which reduces its efficiency. However, the effects of the downwash don't cause as large a problem as the tailplane would experience in a conventional set-up.