Anyway of shooting a pic to us to see and make a better determination. Your right, might be lights a too close but won't real know without seeing it..........
Okay so there's a noobie gap in my knowledge about topping apparently. Specifically with main-lining.
When you say wait 4-5 nodes before topping, are you topping at the 4th or 5th node for main-lining?
Because...
I thought you were supposed to top at the first node, enabling equal hormone distribution split 50/50.
OR.. are you still topping at the first node, just allowing the plant to grow to the 4th/5th node for a maturity and stability type thing?
Which wastes time IMO.
It's actually good that it's warm when there that small just make sure its not to dry..and topping that early is NO BUENO you should wait till it gets some size. I wait to top until my plants are about 5-7 inches tall and have 4-6 nodes