The text of the article from 1936 about this bike says:
Natural streamlining is accomplished in a new type of bicycle designed in England for use on speedways. Aware of the discomfort suffered by racers who must remain humped up over their machines for long periods due to air resistance, the designer has placed the drive pedals behind the rear wheels. The handlebars are lowered almost to the level of the front axle.
In this posture the rider is almost horizontal to the ground and in a naturally streamlined position. It is believed the new machine will produce speeds far in excess of anything yet accomplished.
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In theory, a smaller frontal area would serve to reduce drag and allow an increase in speed, but it appears the rider is supported over a large portion of his lower abdomen. That would restrict breathing and effectively limit his endurance.
Chris Boardman's 'Superman' position was similar in that it reduced frontal area, yet allowed for better breathing.