It’s all a balancing act.
I find even with the DLI raised, if the lights are to far away the plants stretch. But maybe I’m just stoned… Early on I need to use a heater as well, but after a bit the plants get big enough and the lights are turned up enough that they seem to capture more of the heat and hold it so a heater isn’t needed.
Currently I have a 240w maxed out and about 15" from my seedlings Im giving them roughly 45 DLI and they are a week old. Yet I still need a heater because it’s winter, I have the exhaust fan set to only kick on if heat rises above 80f roughly.
The biggest thing with DLI is to ensure your at least getting that much, so give them at least 15 for now.
If you give them more light that’s fine, just realize it may keep them short and stocky which is a pain if your trying to scog or lst.
However you don’t need to scog or lst to grow, and some strings stretch alot so hammer them with more light until they show light stress (Crispy leaf edges or bleaching of tips).
This will use more energy and thus produce more heat reducing the amount your heater is in use but still costing you near the same energy most likely.