Hey, I currently veg under a 400 MH, too. Since you asked about distances I have mine at around 40cm away from the tops of my plant. I even have a seedling there (in 45cm distance) that received full hard light from day 2 after I had it transplanted from out the water. If healthy enough even immature plants can metabolize the full thrust of artificial light (...or the sun).
I keep my lamps on 24h throughout the whole veg and basically put anything under it, seedlings, clones, vegging. Indoors the light-intensity can be easily controlled via distance. This way I encounter less problems with sativa-dominant strains (amongst other things...).
That seedling is just about 5cm farther away from the MH, but because light diminishes in strength inversely proportional to its distance, that can make a huge difference.
I mentioning this because I believe -judging from the pics you hosted- none of your plants did receive heat stress or light stress.
Heat stress means the leaves closest to the lamp has its ridges curled upwards. Light stress can result in bleaching that will create big yellowish/white dots or areas that are entirely dry/dead. If you're not sure if you should hang your lamp closer simply try it out, in 5cm steps, every day. Everytime control for above symptomatics.
If you're breeding different strains (like I do) you can "test out" the minimum distance a strain needs to a particular light and make a notice. Since light travels longer diagonally I always use some CLF to illuminate specific spots (corners...) and also have pots at a different height: outward pots are elevated: The "Sweat Spot" of your MH lamp encircles it in all directions. You make your plants grow into this circle using LST etc pp. Especially if you have different genetics you can make good use of low/high-vegging plants (you see I have all bigger plants away from the middle spot...)
The metalnut + coord dangling from the MH is there for height control. It shows me a 40cm mark, although I made knots for other wattages also. HID lamps get VERY HOT you need to be careful not to incite a FIRE with such rope! The good thing about it is that you can move it around rather freely and then also control distances diagonally.
But coming back to your plants:
They don't look that healthy. The leaves are too droopy, esp. the one in the right upper corner. It could be you just water them and it still needed some time, it could be only a minor issue that is already gone. If you give them enough light and don't drown them in water they should recover. They should also be able to get access to new soil and then develop leaves which are less bright. But some of the older fan leaves which are showing necrosis will ultimately die, there's nothing what you can do about it.
