The tenth house is a pivot, angular, and its Hellenistic name is Mesouranema, the Midheaven. Counting by whole signs it stands square to the rising sign and is configured to it.
The name conceals a genuine split. In the quadrant systems the tenth cusp is the Midheaven, the degree of the ecliptic on the upper meridian. In whole-sign and equal houses it is not. Equal sets the tenth cusp at 270 degrees from the ascendant, and whole-sign gives the tenth house to the tenth sign from the rising sign; in both, the true Midheaven floats and commonly lands in the ninth or the eleventh rather than the tenth.
So a chart can put a planet conjunct the Midheaven and place it in the ninth house, and this is not a defect of the system but a property of it. The meridian and the house division are two separate structures, and only one family of systems fuses them.
There is a second thing worth knowing about the Midheaven itself. It is not the highest point of a planet's daily path, nor the same as the culminating degree in azimuth; it is the intersection of the ecliptic with the meridian. At high latitudes the ecliptic can stand at a very shallow angle to the horizon, and the Midheaven can then be surprisingly close to the ascendant, compressing three houses into a narrow arc in the quadrant systems and producing very uneven houses.