What do you think, you put a light in there and you have 14" your going to need somewhere for the roots to grow so you got 4 " of medium. Now you have 10" of grow space.
Think Bonsai man. use a 2" container to bound the roots and start your light cycle off at 12/12 dont try and veg. when it gets too close to the light, bend it.
Oh yea, its ok for the leaves to touch the sides.