The quality of the new lamps?

it doesn't use PPFD correctly... at 30cm, but it's the footprint that matters not the height... usually can assume a fixture will direct light in correct direction :P it's 600umol/s for 240w (2.5umol/J, if accurate) based on diode count, good chance it is LM561 samsung chips. probably accurate in most respects, if that is the case. This will be 1200umol/s in 1 m^2, which is 1200ppfd, but not all of that hits the plant, which is what matters (below).... not "ppfd at 300mm".. You are well above a reasonable max for ambient CO2 - if you aren't supplementing any co2, you have a good cushion above need for 1 m^2. The height you choose should be mostly about footprint. raise it a bit higher to cover edges and corners better if it makes sense. even with a bar-style light yu may want 18-24" even though you can get closer without burning them. Now, how it is dispersed and defracted is another part of that equation. there will be hotspots that go above "1200ppfd" relative to a small space in tent and obviously the corners will be much lower, but it will average out. how spread out the light is will help even that out. You'll lose some of those photons to the walls (7-15% absorbed each time it bounces) no energy or mass is ever lost or gained (laws of physics). it might be absorbed or miss the plant, which would reduce that "1200ppfd". certain factors can increase that loss (height from canopy, for example, even though it may be a net positive due to more even coverage in some cases). Check out a DLI table. you really only need about 40DLII in a day with atmospheric CO2 + random temp/RH%, possibly less... you can see why i say you have a healthy cushion. that will be around about 900 ppfd over 12 hours/day covering 1m^2. if adding co2.. you may not take full advantage of say 1200ppm, but could use some elevated amount without wasting it.