looking good brother P, have you determined what you think the yellowed tops are from?
You may dock your lights back another 6-8", that is a split image of what I had just saw with my '12 51's @ 12" and the difference of a few inches is night and day
We're providing some serious levels of PAR light, especially in Cab/closet/stealth grows- that PAR gets very concentrated,
Rosenthal stated that Water, Nutrients, Light, Temp/RH, and CO2 are the five limiting factors that we need to worry about. So even in a perfect system- right temps, nutes are good, but limited CO2- we may not be able to take advantage of all those extra photons flying around- without CO2. When the kids cant take all the light we're giving em... we get chlorosis. Look at it like your wpsf and HIDs when you're considering CO2- you are at the brink of that decision. Know'm'sayin?
I ended having to keep my 195w 51 at 14" (min) in veg at all times before the yellowing, and my 390w of 51's at 20" in early flower- but able to be brought down to 16" once they finish the transition and start bulking up
Just some food for thought, happy growing bruv!