Once you set the load via the tightening screws on the stem, the cap shouldn't really come into play - in a perfect world.
In reality the tight stem cap would assure less possible slipping/loosening of the stem. So, I always prefer to have the stemcap snug to the top of the stem, providing a little downward 'insurance'.
I'm not familiar with that particular config, bit it works just like they all do - and need some small space between the top of steerer and the stemcap, when everything is properly set.
Simplest solution I would use:
Add a mm or 2 of spacer to allow the stemcap to snug down to the stem.
If you can't get a 2 mm spacer of that shape... I would go to an office supply shop - purchase a plastic three-hole binder in black - those plastic covers are usually 1mm to 1.5mm thick.
Take a spacer and trace the outside outline of the 'carbon' spacer onto the plastic cover sheet. Cut out to match, cut the inside appropriately (doesn't need to be exact.
Insert additional thin plastic spacer somewhere into the spacer array. Tighten all up - should be enough to be able to tighten the stemcap to the stem top.
If not enough... cut another spacer and add... No one will ever notice, only you will know...
Ride the bike...
Thx
Yuri
EDIT - another reason for a snug stemcap... If you ride ONLY on Sunny days - no worries...
If you ride when there's moisture in the air or on the road, or perspire somewhat, and drip on the bike... you might want a snug stemcap.
Moisture seems to find all small tight spaces... and if there's a chance for some corrosion in spaces you can't see or often reach - it'll happen..