Absolutely do NOT ever put the pinky under. Not only does it distort the rest of your left hand, but you need that pinky up and "ready" because one day you'll pick up some other woodwinds and discover that the left-hand pinky has actual work to do, on top of the bore.
You can place your left pinky wherever it feels comfortable. You can leave it free or rest the tip against the side of the instrument (which gives the recorder a little more stability). Placing it under the instrument would be very unusual.