Joe, I'd be worried if the cops were sitting around, wasting their time and our taxes by positioning their RBT units where there is little likelihood of them busting a drunk driver. Police resources are limited - you use them where you'll get the most bang for your buck. That means - duh - doing breath testing where there are lots of people drinking and driving.
Mention is made of Kings Cross, and how few tests are carried out in that area. Well duh, because parking and traffic in that area are an utter nightmare, if you're going there to get on the turps, you catch the train or a cab. Or you walk. There are no drunk drivers to breathalyse as the drunks are all staggering around looking for a taxi home, rather than trying to remember which backstreet they parked their car on.
Most tests are carried out in the west, where public transport and taxis are few and far between and where the distance between pub and home is too far to walk. Of course there are likely to be more pissed idiots behind the wheel out there. Why am I having to tell you this? Why couldn't you figure it out for yourself? Jeez Joe, are you drunk?
The cops are obviously using their brains, figuring out where the problem areas are and concentrating on those. If they were deciding where to place their RBT units by throwing darts at a map, I'd be really worried.