I emailed CSG about smaller cards and here is the response:
Hello Andy,
For smaller cards we create a custom clear insert to hold the card safely in place.
If you have any questions, please let me know.
Thank you and have a wonderful day,
Justin Hudlow
Customer Service
Certified Collectibles Group
p. 800-642-2646 | f. 941-360-2553
jhudlow@NGCcoin.com