that makes perfect sense. You need a strong IR light source like a 
tea light or candle. Your Mac Mini or TV shouldn't emit much if any 
IR light / great heat and would probably also be too massive as that 
they could be used as a - literally - hot spot for the Wiimote to 
recognize.

The calibration does only kick in after you already have a IR source 
that is strong enough. It allows you to determine in which range you 
want to move the cursor across the screen. But you'll usually not 
need that as Remote Buddy is preconfigured with values good for 
almost every purpose.

You can (ab)use calibration to also see what your IR sensor is 
seeing, though. Alternatively, you can also do this by pressing 
button 1 to activate/deactive the IR mouse mode.

What calibration doesn't (and can't) do is to change the sensitivity 
of the IR sensor. Hardware wise it's possible to adjust it, but you'd 
still need a proper IR source, so it wouldn't be of help here either.

Hope that helps.

Best regards, 
Felix