If they're angled to match the conical frame sides of the bearings, then they're likely shims to raise the bearings, so the top cap has the right clearance with the frame. If the bearing settles in too deep, or the cone presses in more because the steerer is a bit small, the top cap will be lower, and may rub. OTOH, too high and you have a gap for dirt and rain to blow through.
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