Probably just had some air in the lines to begin with. I'm not sure about the '06's but on my '03 the brake lever was not directly attached to the master cylinder (if that makes sense), but with the Satos it is, makes it more sensitive also.
Also, Sato rearsets (or at least the ones I had) have adjustible brake and shifter throw...they have two mounting holes where you can attach the shifter linkage and the brake master cylander, and one of the holes is set farther back so you have to move the lever less to have the same effect. Depending on where you put it, you could have shortened the brake throw pretty significantly, which would make it much more sensitive.
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