Light height? Let's talk about it.
Firstly, LED manufactures use false, inflated "equivalents". That 1200W lamp is probably only 200-250Watts. I mention this because the 200-250W is the number to focus on when it comes to taking PAR and PPFD readings (Buyer beware. Lots of lies from manufactures to appear better then others). Anywho!!! Most LED manufacturers will give you benchmark heights to use in the seedling, Veg and flowering state but I have noticed some very close relationships between all these lamps. With seedlings you're going to want a 60-75cm buffer space. Veg, you're looking at 60cm and Flower is 45-60cm buffer space. I'd check the manufacturer specs, but I can almost guarantee these are the numbers you'll find. Heads up that LEDS are obviously intense as eff and these numbers may not work for you. If they stretch and get lanky, too far. If they cup, twist or burn you're too close. Again, the manufacture has benchmark numbers, but pending on your entire environment you may have to move it up or down to it's "sweet spot".
As for the bloom and Veg switch, this is another manufacturer recommendation BUT most will tell you to operate both switches while in flower. If you find this to intense for the plants, there is nothing stopping you from flicking off the "Veg" switch whenever you'd like.
Quick example from my grow: SF-2000 recommends a 60cm buffer. At this height my plants were being heat stressed and it was obvious. They were cupping, 'praying' and burning. I moved the SF to 75cm and everything was ok. Play it by ear and within a couple days you WILL have that sweet spot you're looking for.
Hope this is the answer you're looking for my friend. I see a couple other issues but you didn't ask about that! so I'll leave it there. Good luck my friend and happy grows✊👍