scjohn,
The resistance in the short length of smaller gauge wire will be insignificant when compared to the resistance of the long run of 2/0. Say you run the 2/0 into the house, next to the panel and end at a j-box. From the feeder breaker into the j-box one might run 4' of conductor. Calculate the actual Ohms of that piece and compare it to the resistance of the 2/0.
The voltage drop along the lighter gauge wire will be inconsequential.
Placing the short section of light gauge at the beginning, middle or end doesn't change the IR drop on it.
