>And if indeed we pool all Brahmins jātis together, I had thought that this pool ends up representing substantial percentages of population in given regions.
Dear Prof. Arlo Griffiths,
 
Can you elaborate more on what you mean by all Brahmin jatis?
 
Among Telugu speaking Brahmins, there is the distinction between Vaidikis (Brahmins who did not move into administrative occupation) and Niyogis (Brahmins who moved into administrative occupation). Similar such distinctions appear to exist in other parts of India too.
 
Are you keeping such sub-caste categories in mind?
 
At least in south India, there are a big number of villages where there is no Brahmin of any variety.
 
The small percentages of Brahmins shown for statistical purposes are all from census where a person belonging to any sub-variety of Brahmin to have claimed during census enumerations to be non-Brahmin.
 
You probably have some other kind of data in mind when you say Brahmin jatis. Can you please elaborate?  

--
Prof.Nagaraj Paturi
Hyderabad-500044