The ninth house is an apoklima, cadent, and its Hellenistic name is Theos, God. Like the third it is cadent and, unlike the sixth and twelfth, it is configured to the rising sign, standing at a trine to it counting by whole signs. Cadence without aversion is the reason the tradition reads the ninth as a place of consequence despite its weak position.
It carries a structural feature that catches out readers moving between systems. In whole-sign houses the Midheaven is not the tenth cusp; it is a degree that falls wherever it falls, and at many latitudes and rising signs it falls in the ninth. A chart cast in whole-sign can therefore have its Midheaven, the most public point in the figure, sitting inside the house of religion, travel and higher learning. That is not an error and it is not a rarity; it is a normal consequence of separating the meridian from the house scheme, and Hellenistic practice accommodated it.
Under Equal houses the same thing can happen, since the ninth cusp there is 240 degrees from the ascendant and the Midheaven is unconstrained. Under the quadrant systems it cannot: the Midheaven is the tenth cusp by definition.
On the ninth cusp itself the quadrant systems divide the arc from the descendant to the Midheaven into three, each by its own rule, and their answers can lie a sign apart in the same chart.