Kenlee, perhaps you might answer the same question?
Certainly the East Asian parents of one of my children's friends suggested that they had moved their very bright child half way across the world because they wanted to AVOID the extreme academic pressure in their home county and were seeking a more rounded education. Oddly I think they would have been put off a school if they thought there would be significant numbers from the same county whose game plan was to spend two years in the UK to gain the grades and English needed to apply for top flight US and English Universities, without taking part in wider school activities. .
In short, I don't think the issue, insofar as there is an issue, is one of race but of culture, and even then I think there is only an issue if groups within the cohort have very different ideas of what boarding education is about, and fail to work well to deliver a constructive, diverse and international community.
Ditto Russians. The ones we have come across have been popular and mix well. We have heard the odd story, which may well be true, of very rich students who turn up in an English boarding school rather shell-shocked, and who then find it quite hard to make the transition from a pampered life back home to chilly playing fields and indifferent school food.
So not really about race. There would be a problem if children from a specific part of England, or a specific class were reluctant to mix with others from a different background. The question for schools might be how they deal with any potential cliquishness, caused by taking in significant groups from different backgrounds.