hlg550 distance from canopy veg

Try not to over think things and par meter you don't need one use common sense the hlg is an easy light to use mine is 3000k, never had a problem with stretching of baby plants, had to stake a couple to support them until the stems thicken, what K is your light? Looking at the pics the height is good and 50% also good. It's not necessary to feed bloom nutes and at that age I still have them under a dome with the vent open. I've had my light at all heights from what you got in your pics (no lower) to as high as 48". During veg the chase for the ideal light height will just do your head in. When it's in flower you start to lower the light to that Goldilocks zone and see what you can get away with, I wouldn't leave anything on top of the hlg keep it clean unless you want to nip a bud and test it 😜 good luck! 🐞