Very interesting...
OK, here is where this is used in my area:
You are due north of the airport 5-7 miles and call the tower inbound, expecting to land on 27. They reply, ?Report 2 mile right base for 27?. At this point, you are cleared directly to base leg from your present position (no downwind). Here is where the confusion begins ? MY base leg is less than a quarter mile from the end of the runway, and in fact I am normally on final (wings level) for only a few seconds before I round out. In other words, I fly a tight pattern. This is significantly different than the students in the 172s flying their huge, FAA approved stabilized approach, and different also from the fire bombers returning from a mission with an even bigger pattern. The point being, the ?location? of the base leg relative to the runway is dependant upon the aircraft to a large part. The only constant is the fact that base is 90 degrees to final, and to me, a 2 mile base means I?m 2 miles away from the extended centerline, along my base leg (put another way, 2 miles to fly, then turn final).
Further support of this position was my experience last week making an approach from the north, expecting to land to the west on a 12,000 foot runway. Since I knew I was parking all the way at the west end, I requested a ?midfield base? and a long landing. This was approved, so I aimed right for the middle of the runway (on an ?extended? base), and called 2 miles before my turn to final (at midfield).