A 6 mm offset on a wheel will push the front face of the wheel outwards, on a very narrow wheel like a minilite this is exactly what you want. On a big fat wheel with a 6mm offset the front face of the wheel will sit even further out away from the mounting surface on the car hence the need to increase the offset. The offset figure relates to the mounting surface of the wheel in relation to the centre point of the width of the wheel, and doesn't relate to the car. Change the width of the wheel without changing the offset will still move the front edge of the wheel closer to the center line of the car (it will also move the inner edge of the wheel out the same distance)
As the trolly jack didn't work, I can only assume this was a safety feature not included by other manufactures, that allow you to jack a car up to a height which you could potentially drop a car on your head, hence By not lifting the car it is safer than all others. However this is not technically a jack; more a door stop so maybe the trades descriptions act should have come into play?