By "natural harmonics" I mean notes at the resonant frequencies of the instrument. Several of them are obviously different from equal temperament, which means t

By "natural harmonics" I mean notes at the resonant frequencies of the instrument. Several of them are obviously different from equal temperament, which means they will sound bad when played with other instruments. When brass players talk about "good intonation", they often mean adjusting these notes into equal temperament with valves/slides/embouchure/hand stopping. Because brass players actually have to pay attention to the tuning, I wouldn't be surprised if they were more sensitive to it than people who played fixed pitch instruments like piano. The Britten piece is notable for the parts where the horn player is instructed not to adjust the pitches to equal temperament, and because it's a solo it still sounds good.