Smaller active area for circle shaped Custom button
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I have a  custom button (which uses a a circled shaped image as its custom view). The problem is: the active area of the custom button is much too large, if I tap at least 100 pixels outside the button, it still gets registered as a tap on the button. This results in accidental taps. 

Note:- I don't want to reduce size of button as it is already bigger that minimum requirement. I want to reduce tappable space.

***How can I reduce the active area on these buttons?***