I don't have the files in front of me (yay work), but whenever an image is spliced in the brush file it follows the same rules: [x,y,x-offset, y-offset], with the initial x,y coordinates being the top left corner of the image chunk (your icon in this case).

So if the brush file defines a block [0,0,100,150] that means the chunk of the image it wants starts at 0,0 (top left of the overall image file) and is 100 pixels long by 150 wide (your bottom right x,y will be 100,150 in this case).

[32,50,120,67] would mean it starts at 32,50 and ends at 152,117.

Hope this helps