First, the passenger sizes were defined from ticket sales data. Then facial bone structures were dimensioned to determine the most appropriate shape and geometry of the headrest elements.

Users trials were held to develop the design. Here we see that because people sit slightly forward to talk, the wing can be longer than might have been supposed, to give better comfort for sleeping.

Also we see that too much wing deployment can interfere with the back of the head, which is pulled away from the neighbour slightly during conversation, because of the narrowness of economy class seats.

Finally, a drawn specification was produced, with dimensions and notes. This was used to refine the aesthetics in conjunction with an industrial designer, then the approved specification was passed to the seat manufacturer for engineering development.  Shown here in miniature is the plan view: