Not necessarily.Plant height at maturity is pretty set by genetics. Plants vegged for 3 to months do not double in height under HPS if they have been properly managed.Because they would be at their maximum vegetative growth stage. Otherwise people would veg Malawi Gold until it was around 12' and then flip it for monsters. The stretch comes in plants flipped early as they attempt to reach their maximum height as determined by genetic code.If you have 4 ft of vertical space I would start to flower around 1 1/2 ft or 2 ft as most of the time (depending on if its an indica or sativa) they double in height when beginning to flower.
They look fairly healthy so far, have you fed any nutrients yet?