short plants? help i need info

I've been veggin for almost 4 weeks now and my plants are less than 8 inches what is going on ive been looking aa other people grows and there plants are massive by 2 weeks, does anyone know why this could be and how i coudl get them to grow taller.

ive got 3 white widow under 400w hps its liek 2 feet away from the tops,
fox farm soil they are in 3 gallon pots and i jus started giving them fowfarm nutes temp has been good and ph is fine whats going on with my plants i was gana try and start flowering in 2 weeks but idk fi its worth it i cant have them vegging for much longer cuz im going away in a few months

They look ok to me.You should see a difference in growth soon as youve just started to add nutes. 2 feet away for a light seems like alot , but im just a beginner so im not too sure , maybe someone else with more experience can tell you more.

They maybe in 3 gallon pots but looks like ya only have 1 gallon of soil. Fill them pots up with soil.

if i put more soil on top will the root system grow bigger than with how much soil there is now. Do roots grow upwards too?

if the roots are growing then the upwards growth will slow down until the roots stop growing from what i understand but im a noob i may be wrong

Fill them up with soil. The more soil the bigger the plant. It will not slow growth.