According to Arctic Silver you don't spread it out, just a vertical line.
Unless you are talking about Tinting the heatsink and metal cap.
Squeeze enough thermal compound onto the center of this area to create a small mound. By working the plastic tool (old credit card) back and forth in all directions you will smooth out the compound and work it into heatsink. This will ensure optimum filling of the microscopic valleys in the metal where the CPU cores will contact the heatsink.