Here's a simple illustration to demonstrate the problem with the rear suspension set up that micras have. To prevent the axle being offset too far as in the second picture when the car is lowered, you should get an adjustable length panhard link.
|Panhard link (blue) when suspension is fully uncompressed and standard|
|Panhard link (blue) when suspension is either compressed or (lowered and uncompressed)|
As you can see, in the second picture, if you simply put shorted springs in your car without shortening the length of the panhard link, your rear axle offset becomes too great, and the left wheel becomes further in under the guard while the right wheel protrudes further out past the guard.
An adjustable panhard link will enable the axle to have a decent starting offset even while the car is lowered. There's nothing you can do about the axle offset increasing as the suspension is compressed ie when hitting a bump, however if you set the offset up correctly when uncompressed, its not an issue as it doesn't change enough to worry about when hitting bumps etc.
Additionally, from my discussions with Whiteline Automotive after overhauling my suspension, they told me that lowering without an adjustable panhard rod also had a terrible effect on the rear axle toe. This makes perfect sense, as its a multi-link design, when the axle offset changes, so does the rear axle toe. Basically one wheel's toe was almost straight while the other had massive toe-out (terrible for handling and tyre wear).
More advanced designs like the "Watts link" featured on solid axle rear wheel drive Ford Falcons combat this problem by a weird swivel type link mounted in a central position. This eliminates the one-way axle offset issue associated with the panhard link design.
The panhard link design allthough frustrating at first, is simple and easy to make perform well.