I was always under the impression the turbo and non-turbo racks were different.exactly. As woo mentioned and is the same in the US, n/a has ESPS (engine speed sensing power steering) and the turbo 2WS has ECPS(electronically controlled, velocity sensitive power steering). I believe 4WS does not have this feature but has a different unit altogether?
The ECPS control unit controls a solenoid valve on the power steering rack. The ECPS control box has a self diagnosis function (with a whole set of malfunction codes) and the switch on the box is also documented in the Mazda Factory Workshop manual. It says :
Steering effort can be varied by the slide switch on the power steering control unit. (approx 10% variaton at 10km/h (6.2mph) or more)
If heavier steering effor is required: H setting
If lighter steering effor is required: L setting