Does anyone know what the optimal toe settings are for the Sierra and Escort Cosworth, and especially why?

I know that it's always said that the setting at the front should be 2 mm toe in and on the rear 3 mm toe in. These are the same numbers Ford gives in the Group A and Group N manual for the Escort Cosworth. The thing I wonder about though is what is 2 or 3 mm toe in exactly? When I have the car aligned it's always measured in degrees, which is a good unit for alignment. For calculating the 2 and 3 mm back to degrees you need to know what rim size it's based on.

So what is the rim size it's based on? For the Sierra I assume this would be 15", but the Escort Group N manual talks about 16" and the Escort Group A manual about 17". And if you even look at the Escort WRC manual it says 18" rims.

Coming to the Escort WRC you also see different toe settings, 0 mm for the front and 2 mm toe in for the rear. Less toe in on the rear (3 mm vs 2 mm) I can understand because the WRC rear suspension has less bump steer. But why would the change the setting for the front from 2 mm toe in to 0 mm? Because as far as I know the front suspension setup is the same for all.