Hi Dude, if you only have 4' You should start early 4 to 5 nodes. I have a 400 hps too and about the space. I am just now understanding that you get the same thing from a 12'' to 18'' plant as you would from a 3' tree. You need to grow indica's. Unless you do a scrog. When you grow top light only you light the top 1/3rd . 1' or 3' doesn't matter. Seems like you woud get more but your only going to get what your light can maintain. Sativa's are tall and you need side lighting. What are you germinating ? Can you keep it cool ? I have a thread of my first grow not too far back give it a look.. I'm upgrading my light and going sog I got every thing coming together and will do a thread. Share some pic's it helps. I just saw the top new grow grapefruit. If I'm not mistaken that is a mostly indica strain I almost got it but did not have the bucks ,oh well. IT stays really short from pic's I've seen.