Position your iPhones around the actor depending on the optimal camera setup.

Check the link below to learn more about capture volumes and iPhone placement. https://help.move.ai/en/articles/8867179-capture-volumes
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The capture volume is the available space for the actor to move around whilst being tracked by the system.

Use the host device preview to mark out the capture volume. Walk towards an iPhone, checking how close you can get whilst keeping your entire body in the frame. Mark this point out on the floor.

Repeat the step above for each iPhone in your setup. This will give you a marked-out capture volume.

Now you can start filming.