CFL's can be as close as 3". Just thinking, Your used to faster growth so maybe you should get some foliar feed going on. Foliar feeding is how I maxed out my first grow. I used a very weak solution about once a day. Be always diligent though for nute burn signs. Starting with burnt tips, progressing to the sides of each finger, finishing with total destruction. care is needed for this. two bottles, one with plain water the other with the nute solution.
After the foliar feeding dries, it leaves a residue of any un-absorbed nutes, it should the be sprayed with plain water as a sort of leaf rinse.
It looks from the pic like maybe your suffering from some nute burn now? Are you using hot soil(high nutrient content)?