In setting toe, you're really looking for an angle from straight ahead. You need that for two reasons: The positive camber makes the wheel naturally want to toe out, which needs to be counteracted, and that affect will take up any slack in the linkage and allow the wheel to turn a little to the outside.
The designers take these factors into account to figure out how much toe-in the vehicle needs to result in the angle they want. With bigger tires, you theoretically need more toe-in to get the same angle. How much is a guess, though. What you do is set the toe in and then check it periodically by feeling the tires. Rub your hand across the tread in both directions. If you feel your hand being grabbed by the edges of the tread blocks more in one direction than the other, you need to change toe in. That condition is called "feathering" and it's a sign that the tire is being dragged slightly sideways as in rolls forward. When there is no feathering, the toe is right for your setup.
