Bigger drag area for sprite

So I have this sprite which is 42x42 in size, but more than half is transparent. The user is supposed to drag it around, but it's kind of difficult. Seems that even if I place the mouse in some non-transparent area, sometimes it still misses it.

My question is: how can I make this sprite's "drag area" as big as the sprite itself, 42x42, without removing transparency?

Thanks!

Does it have something to do with the bounding box around that sprite?

Yes the bounding box (aka collision polygon) is taken into account on drag and drop too. Thanks!