I think he's talking about taking 2mm of material off the front of the arm where the inner pin goes through and adding 2mm of shims behind the arm to get a shorter wheel base.

But then that angles the cva different so the jack on the rear end has changed. Didn't want to write it out so I stole from Tekno, they are talking about the front, but its doing the same up force or down force for the rear... angled forward will resist squat.

When the driveshafts are swept forwards, the stub axles are being twisted down toward the ground, pushing down on the tires and lifting the front of the chassis. This can be helpful in really bumpy sections to keep the front up and not dig in. It will also create more weight transfer to the front during braking which will increase your off-power steering.
When the driveshafts are swept backwards, the stub axles are now being twisted up, lifting the tires and pushing the chassis down. We've found that the biggest benefit to sweeping the arms back is jump landing. With the arms back, the car kind of "sucks" itself to the ground. It settles much faster and allows you to get on the throttle immediately. During breaking and off throttle the chassis will stay a little flatter front to back and either feel "pushy" or more controlled into the corner.