Shouldnt parallel leaves be parallel??

In very simple terms I think of it this way...
The front section of the leaf springs are mounted securely to the frame.
The rear sections are using a shackle...therefore the front sections are locating the axle while the rear section provides the springing action. (simplified I know...but...)

The rearmost springing part pushing on the extreme outside and rearward part of the structure should limit the leaning in turns while having the springs closer together at the front will be unnoticeable...think torque tube. Pivots at the center...no effect on handling at all. Its a very early style of bodyroll control.

Having the rear of the spring higher than the front is to control "Rollsteering".
The front section of the spring needs to be basicly parallel to the ground so that the axle doesn't get pushed back as the car leans hard in a turn. That would cause the rear to turn the car sharper into the turn and potentually spin.
To make it work, the arch of the spring needs to be compensated for, so the rear of the spring pack has to be higher than the front.

All of this positioning stuff is part of the engineering of the chassis. It isn't a hit or miss thing...and there are a million variations over the years!