Struggling to distinguish European vs Brazilian nasal vowels in audio logs

I’ve been recording myself reading out loud to fix my accent, but I’ve hit a wall trying to nail the nasal vowels like the 'ão' in 'coração'. Since I'm aiming for a neutral European Portuguese accent rather than Brazilian, I find that my recordings still sound way too 'open'. Does anyone have tips for mouth positioning differences between the two variants, or specific drills to stop me from slipping into the Brazilian pronunciation while practicing?