This profile pairs the fifth and first line positions of a hexagram, separated by two positions counting round the six, and it is one of the twelve ordered pairs Human Design admits.
The positions in classical commentary
The fifth line is the central line of the upper trigram and conventionally the ruling position of a hexagram, the best placed of the six in the commentarial tradition. The first line is the bottom of the figure, the beginning of the situation, read as obscure and not yet able to act.
Those are readings of positions within a described situation. The Yijing tradition does not use them to classify people.
Why twelve and not thirty
There are thirty ordered pairs of distinct lines. Human Design uses twelve: the six ordered pairs whose lines are separated by three positions, and the six separated by two. The separations of three coincide exactly with the Yijing's doctrine of correspondence between lines one and four, two and five, three and six, which is a genuine structural inheritance. The separations of two, of which this is one, have no counterpart in that doctrine.
The modern layer
The role names attached to the six lines, and the reading of a pair as a personality, are Ra Uru Hu's, published in 1987. The atlas records the inherited structure and the modern interpretation separately.