@DutchHolland
Thank you for posting on the HP Support Community.
After reading your post, I did go through the Maintenance and Service Guide of your product and found that you have one fan with UMA graphics memory installed on the PC.To get the answer to this question, the extra space/cut out what you're looking at it is for additional fan.
(refer to the 64 Chapter 5 Removal and replacement procedures for authorized service provider parts- Fan.
Hope this helps! Keep me posted for further assistance.
Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution.
ECHO_LAKE
I am an HP Employee