The Bambino Plus is setup to extract a certain volume. I also was getting about 40-45 ml out of the box. The manual tells you how to program whatever volume you prefer. Once you enter program mode (hold both shot buttons down for 2 sec...they will blink a couple of times). Press the 2 shot button and hold for as long as you want pre-infusion. Watch a shot glass fill until desired amount. press button to stop.
I have mine at 8-10 sec pre-infuse (depends on grind, erc.), then stops once it gets to 60 ml. Doesn't seem to matter if I grind my coffee or my wife grinds her decaf...still get the programmed 60 ml. Different times, though (so can play with other factors to adjust time).