"Middle class", "upper class", etc. are not defined by percentiles. Otherwise it would mean nothing when we say a particular country has a "growing middle class".
If they were defined by percentiles (i.e. certain definitions of middle class dictate the middle 60% of the population by income), you could still describe a "growing middle class" as a middle class acquiring a greater percentage of total income. While the population of the middle class isn't growing, its buying power still could be.
Make it about half a million Chinese students in the US currently, so we're talking about the top 1%.