The sixth house carries servants in the medieval catalogue, and it carries them alongside sickness, small cattle, day labour and, in Lilly, uncles and aunts on the father's side. The Hellenistic name for the same place is Kake Tyche, Bad Fortune, and Mars has its joy there.
The company the servant keeps in that list shows how the tradition understood the relation. This is not the house of colleagues, nor of people the native likes. It is the house of what must be attended to daily, of what can go wrong in the body and the household, and of people whose work is bounded by obligation rather than by affection. A reading that treats the sixth as the workplace in a modern sense has softened it considerably.
Read from the other side, the servant's own chart would carry the same relation in its seventh or its tenth, and the tradition is aware of the asymmetry. This is a chart of the native's household as the native stands in it, so the servant appears as a function of that household rather than as a person with a nativity of their own. The derived house method exists partly to correct for that: the sixth taken as a first house gives the servant a full set of twelve places, and the astrologer can then ask about their health, their money and their loyalty separately.
The modern equivalent of the sixth is employment, routine, health and the daily order of work. The change in vocabulary carries a real change in what the house is thought to describe.
Sources Christian AstrologyWilliam Lilly with Hellenistic Astrology: The Study of Fate and FortuneChris Brennan