This is incorrect if you have an ally adjacent to that enemy. If you have Advantage from high ground, and Disadvantage from a far away enemy, then you're attacking at normal (single d20 roll). If you have an ally adjacent to that enemy, you should be able to get sneak attack because you're not attacking at disadvantage.
Ah! If course. Didn't think that the same rule would apply to ranged sneak attack. Meh, so nothing really changed.
