The room modes should be distributed as evenly as possible. Overlapping leads to dips and boosts in the frequency response. Only room modes below 300 Hz are significant. The calculator only shows the room modes of rectangular or square rooms.
Axial room modes are the most powerful modes. They are created between two parallel surfaces, i.e. between the ceiling and the floor and between opposing walls.
Tangential room modes hit four surfaces. They have half the energy of the axial room modes.
Oblique room modes have a quarter of the energy of axial modes. They hit six surfaces and are therefore created primarily through the corners of the room.