Make sure that spacers can be used above the stem as well. For example, Cannondale says not use them above the stem.

See page 15:
http://media.cannondale.com/media/ma...rSixEVO_EN.pdf

Assemble the fork, headset, spacers, and stem without tightening the stem bolts onto the head tube. When the system is assembled, the carbon steerer tube should be 2-3 mm below the top stem. All spacers must be located below the stem and within the maximum stack height as shown. No spacers may be used above the stem.

Its different for every bike though. Fuji recommends a spacer above for their setup.