How many microphones are there for bluetooth phone

Hi - does anyone know whether there is just one microphone in the latest Nissan Micra that is used to pick up cabin audio during bluetooth phone calls? Driver audio is crystal clear to recipients, but audio is not picked up in any of the passenger seats (ie phone bluetooth only works for the driver). Is this a fault or just a poor design choice to keep costs down?

Other Nissan models (e.g. Juke/ Qashqai) seem to pick up cabin audio wherever anyone is sat in the car, so curious to know if the micra is different, or if there is a secondary passenger-side microphone that may not be working correctly.

Thanks for any insight!