The point of the questions is to determine why it was not possible to make a connection point inside the house. Most houses have a utility room that people can walk into, where you would have the pressure tank and pressure switch. The point of connection would be just past the pressure tank, on the downstream side. The system point of connection would be at the pressure tank, and the supply line would run to an exterior wall, then outside to the backflow preventer.
Why prefer this? Easy access, for one. Also, when you tap a sprinkler system on the upstream side of the pressure tank, the water is flowing in a reverse direction from the pressure tank, every time the system turns on, and that is never optimal.