How to set delta pixels change to detect mouse movement

[jd1008]

Hi all,
Some gui apps have very thin bordered windows, so thin that if I want to 
enlarge of shrink the window, I find it impossible to position the 
cursor exactly on the spot of the border of that window in order to get 
the resizing to take place.

Is there a setting I can place in ~/.Xdefaults  so that I can set the 
delta movement small enough in order to capture the edge of the boarder 
and resize the window?