In this paper, it states:

The leading edge suction of the left backswept wing is larger than that of the right forward-swept wing at subsonic speed, and the lift vector of the left wing inclines forward (see Fig. 2(b)), which results in smaller drag of the left wing.

What causes the left back swept wing to have more leading edge suction? For clarity, this is an obliquely swept wing:

What is different about the right forward swept wing compared to the left back swept wing? Why does the left side have a higher amount of leading edge suction?

It also states that at subsonic speed this is true, which to me, hints that this is false at supersonic speed.