more light... proper levels of nutes -- e.g. do not treat it like foie gras.
CO2 is you limiting factor. 35-40DLI might be max amount of light per day you can provide in ambient co2, but in a controlled environment with boosted 1200-1300ppm co2, you can give 133-150% more light per day. 50-60DLI... it's a diminishing return as you go up, though... at some point squeezing in a bit more light won't be worth the extra cost relative to what it adds. 55-60DLI is about as high as you want to go and better have lab-precision control over temps and RH% to fully maximize all that extra CO2 or you are just pissing money away for an ego boost.
In the end genetics will mater significantly and you'll observe variance in growth rates... More genetically depressed (more inbred) plants will grow more slowly. i have 4 strains that recently sprouted... the hybrid of 2 unrelated plants is outpacing the entire room and they were one of the last sprouts, so a day or two yunger at this stage is still significant, yet they ae larger than everything else already in a significant way. inbreeding is a HUGE factor to vigorous growth.
so many factors go into it it is hard to attribute what the cause is without indepth knowledge of the plantn and its background. An "F1" is going to be more vigrous than an "S1" etc... but may not be as consistent.
in the end what we do is 5-10% of the total pie.. what we do whle growing the plant is more accurately described as trying not to step on our own dicks along the way. avoiding mistakes is more important than some mytical/magical product someone adds... if oyu feed well you wont see symptoms.. through trial andn eror you can find an upper boundary for any particular nutrient and then dial slightly back to avoid leaf symptoms.. (same with lower boundary, but our goal is to push upper boundary) This will fluctuate relative to amount of light provided, coww available, temps, rh etc... so many factors.. the more consistent you are with the ancillary stuff, the more confident you can be about learning those upper limits of nute concentrations and nute ratios used. The plant can only use so much per day... force feeding more will end in a toxicity which likely isnt a positive.