Air intake is at the front of the Black Lid.
If you turn your Mac Mini upside down
and press along the edge of the circular lid
you'll fee it is firm all the way around
except where the locked / unlocked dots are.
That gap is where the air enters the unibody.
It flows down through the WiFi antena's swiss cheese holes
over the logic board and then up to the blower fan's air intake;
cooling the board components before it cools the heatsink on it's way out.