You need an expanding plug in your steerer to allow proper headset adjustment. These plugs are used in place of a starnut which is not to be used an any carbon steerer unless the fork maker specifically provides a suitable one. FSA and Profile designs both make suitable expander plugs.
Once the fork is installed, any spacers added and the stem slipped on loosely, the top bolt in conjunction with the expander, is used to set the headset adjustment. Then, and only then, do you tighten down the stem's clamp bolts.
BTW, I have aluminum stems on two carbon steerers and have never used or needed assembly paste. I tighten the stem's clamping bolts to the lower end of the specified torque range or even a bit lower and have never had the stem slip.