why does my bot keep dropping its accent after a few messages 😭

my character is written with a really specific posh british voice and it nails it for the first dozen messages then it just… flattens into boring neutral narration and never comes back. i put dialect notes in the definition, added example dialogue, everything, and it still drifts. is this a memory/context window thing or am i writing the instructions wrong? this is driving me up the wall