Let's look at admissions to top PhD programs in English, where it seems like the top 10 schools each receive about 300 applications for an average of about 6 spots (these are approximations only). Across this sampling of schools, assume that there are 600 unique applicants. If all schools select different candidates, which admittedly is very likely not the case, the chances of being admitted to a top 10 program bounce from something on the order of 2% to more like 10%.
How overly optimistic is this calculation?