I am just regurgitating information from other members here but here is the way I understand it.
DLI is the goal and I follow this chart
I found this
Here.
Then I use
this calculator to figure out my DLI.
From what I understand raising your light physically in the tent and increasing power to achieve your desired DLI gives better penetration through the entire grow area than lowering the lights closer to the plants and decreasing power to reach your DLI goal.
I could be way off base here but this is the theory I am using for my current grow.