There are a lot of things. The device's antenna pattern and orientation are a big part. Metal in/around any of the devices. Signal/Noise. etc. You can try to

There are a lot of things. The device's antenna pattern and orientation are a big part. Metal in/around any of the devices. Signal/Noise. etc. You can try to improve with a lot of calibration but it will also be subject to noise from every audience members bluetooth radio too.