I'm considering buying the following product for a security floodlight install: Arlington 8141-1 Vertical Siding Lamp Mounting Kit with Built-in Box for 1/2 Inch Vertical Siding LAP. It seems to get great reviews, but I don't understand how this can possibly follow code. It features a round, 4in diameter x .5in deep j-box. In the simplest case, it would require six wires to connect a fixture at the end of the cable run (three from the NM cable, three from the fixture). However, six 14-gauge wires would require a 4in round j-box that is 1.25in deep according to NEC.
Can someone please explain to me why this j-box is acceptable or not? Full disclaimer, I'm a total noob at electrical so it's entirely possible I'm just not understanding something properly. Thanks!