The question is: How does changing the spoke cross from 3x to 2x change the bracing angle, and thus the tension?

I stole this image from Andy Muzi's site http://www.yellowjersey.org/, then added the lines. Obviously, they are not to scale, but the relative positions are illustrated accurately.

• The red lines approximately represent 2 cross.
• The blue lines approximately represent 3 cross.
• The black lines represent a rim, and some centerlines: the center of the hub, the center of the wheel.

You can see from the red and blue lines that the bracing angle for 2x is greater than for 3x.

If this were the left side of a rear wheel, this means the tension on the 3x spokes must be greater than the tension on the 2x spokes.

Effects:

Compared to a rear wheel laced 3x on both sides,

• Lacing the drive side 2x and the non-drive side 3x tends to bring the two sides closer in tension.
• Lacing the drive side 3x and the non-drive side 2x tends to take the two sides farther apart in tension.

Note that if the derailleur is already close to the spokes, then lacing 2x on the drive side might bring the spokes into contact with the derailleur. A friend had this happen on his Campy equipped road bike back when 8s was new.