In good spacing of the plants the canopy at about 2 feet blocks all light from the floor. Any more than that is wasted.

Now side lighting and mylar can help with this problem but only so much can be done.

The biggest thing is to know your strain. Know how much the stretch will be so you know when to put them in.

As far as trimming. Trim away in veg but stop about a week before flower. With enough time I have seen one plant in veg 3 months and no more than 36 inches tall container and all produce 5 pounds of bud.

Look into the trimming method of the Phototrons. Not that you can get that from a tron. Just the method is sound.