I drink watered down orange juice. It mixes evenly if you pour the water first.
Otherwise the concentration is higher and the temperature is lower near the bottom of the glass.
Otherwise the concentration is higher and the temperature is lower near the bottom of the glass.
By the same reasoning, tea should actually mix better if you add the tea first, since milk has about the same density as orange juice and tea has about the same density as water. But in the case of tea and milk, you just have to bite the bullet and stir it manually if you want to avoid scalding.