Not what the AO at both Duke and Brown told my kid but I will defer to your experience. This wasn’t regarding NMSF but the schools consideration was based on the prep schools locations were told. Didn’t ask about International so that distinction makes sense.
We were told no geographic benefit given the benefit of the prep school itself was far more meaningful.
I forget which of the two schools it was at but we were specifically told you can’t “double dip” the benefit of going to an elite prep and then benefit from being from an underrepresented state. We also never saw prep school counselors adjusting up kids from Montana or other underrepresented states target school lists and or adjusting down those from more well represented states.
That was our experience at least.