5th Gen Rare Pokemon More Common in Double Grass?

[thegoodguy3221]

After watching videos of Shiny Amoonguss and Route 10 in Pokemon Black and White on YouTube, I can tell that Amoongus, which has a 10% encounter rate, is surprisingly more common in double grass than in normal grass, like around 20-30%. Bulbapedia states that this happens most of the time.