Yeah, the T5's need to be really close at about 2"- 4" away from the tops. Easy on the nutes as that's a pretty young plant. I don't start feeding until about that size or a even a little bigger. Maybe it just looks smaller b/c it's drooping? How is the soil? Does it dry out in between waterings?
I grow in low humidity too. My room is typically 20% RH and goes up to 30% on humid days. I know it's easier to grow where it's in the 40-50% range as they don't use as much water but I've had no problems except when I cure. That's when I run a humidifier in the closet @ 50% RH.