Generally running less than the standard riser plate will give you more traction on that end of the car. However, there are situations where it can give you less traction. Unfortunatelly there is no way to tell until you try the other options and know what to look for. What you are dealing with in this case is not an increase or decrease of rear traction. You are dealing with a increase or decrease in front traction because your chassis is able to roll more because of the rear roll center change. By allowing the "rear" to roll more you inadvertently are transfering more weight (left and right) on the front end also (remember it is a stiff chassis right?). This should be why you got more steering. Unfortunately, NO ONE can tell you what an adjustment is going to do. They can only give you advice, and their personal experience.
Ignaranuses can stop reading at this point.
This is why people get confused when they make an adjustment and the car doesn't do "what it is supposed to". As if the car has a mind of it's own and it is secretly plotting against you. "Fu## no I won't do what cha told me!" The car does exaclty what it is supposed to do with the setup it has on, unless it is broken, it has no choice. When it doesn't work the way you expect, it is because you don't understand what is happening. These are, as far as I am concerned, the most important tuning experiences you can have. This is because you are forced to understand that which doesn't make sense.
(Okay, now in your best yoda impersonation repeat after me- "Smart you will become, for now you are not.)
Anyways, Schumacher makes (made) many sets of alloy blocks that will fit on the Mi2 (mostly from the fireblade series of cars). When did you buy the blocks? (are they new?) The best thing to do is measure it by holding the chassis verticle (rear end down, body mount off) on your tweak board and use a camber guage to tell you how much toe you have.