The answer is to not make a crosshair, make an L.
The upper left hand corner on the mouse pointer is the aim point.
So make a custom one that has a vertical line down the left side, a horizontal line across the top, and a angled line from upper left to lower right.
Gives you a handy dandy mouse pointer that has a nice clean point for aiming.
Also you can make it vivid green, purple, etc for visibility.