Originally Posted by
grolby
Huh, I've always heard the opposite - that you should have a small spacer above the stem so that torquing the bolts doesn't crush the end of the steerer, which is the weakest area. Either way, I wouldn't worry about it unless you have more than 2 cm or so of spacers stacked above the stem, or more than a couple mm of the stem stick up above the top of the steerer.
As usual Merlin is correct and you are misinformed. Too many spacers above the stem clamp displaces the steer expander higher. This doesn't allow for the expander to reinforce the ID of the carbon steerer tube in the area of highest stress where the stem clamp bolts are torqued...or below where the lower edge of the stem clamp induces a stress riser due to handlebar torque applied by the rider.