The likelihood of transmission depends not only on the distance, but also on the time spent in proximity to the source. I read that a few minutes at one metre is no more risky than an hour at 2. ( I may have got the exact numbers wrong). You could argue that there is no safe distance within a 737/320 over a three hour journey.
A lot also depends on air flow in a confined space, such as a plane.
A group of cases traced to a dining area in Gwangzhou had some cases at several metres, because the ventilation system blew air that way.
And the original spreader was symptomless.