Three-Phase AC Magnetic Field

Three conductors carry the following AC currents:

$I_A = I \, sin(\omega t) \\ I_B = I \, sin(\omega t - 2 \pi / 3) \\ I_C = I \, sin(\omega t + 2 \pi / 3)$

The currents flow into the page, and the conductor geometries are shown in the diagram. There is a test point to the right of the conductors.

The peak value of the magnetic flux density $(B)$ at the test point can be expressed as:

$\large{B_{max} = \alpha \, \frac{\mu_0 \, I}{2 \pi }}$

What is the value of $\alpha$ ?

Note: Neglect the thickness of the conductors