Your type of casefan may not travel far enough to reach that spot in a meaningfull manner at your chosen rpm.
In HWinfo your motherboard temps are usually a good indicator how cozy that ssd slot has it.
I consider this a good/average range:
If the Motherboard gets above 40 degree C you can count this as a valid indicator for a deadspot in your airflow (around your ssd spot).
An ssd cooler with heatpipes and/or a fan may have to be added.
With vhb tape you can slap a fan on everything, even missusing your aio underside to mount one
One last thing:
The tinkerer in me asks if you can measure a difference in temps by only closing this gap?