How do deep-seeking "two-box" metal detectors work?

There is a type of metal detector known as a "two-box" metal detector, which is able to find much deeper objects than a traditional metal detector. The back coil is often referred to as the transmit coil and the front coil as the receive coil. However, the transmit coil is rotated 90 degrees so that the flux lines are no longer perpendicular to the surface of the earth. How do these detectors work? I am having trouble understanding the physics of this.

I think what is happening is that the transmit coil is orthogonal to the receive coil so that no flux from the transmit coil passes through the receive coil. Then the transmit coil generates an alternating magnetic field, which induces eddy currents in the metal object, and the receive coil is then able to pick up this correlated oscillating induced magnetic field. The two coils are spatially separated so that the field lines from the transmitting coil enter the metal object at an angle that is also "visible" from the receiving coil (i.e. the field lines passing through the metal object are not orthogonal to the plane of either coil). Is this correct?

White TM-808:

Fisher Gemini-3:

Nexus Pathfinder Version 2: