What device did you use to measure this PPFD of 410?
The PPFD is based on the PPF. PPF is based on 2.3 umol/j which is well known to be the output of those emitters at 2.1 amps. 410 would be the average so it would be higher in the middle and lower at the edges. Light height over a 3x3 should be about 20 inches.
When I was growing, one of the lamps I used had a veg setting, 740 PPFD at full power and 450 in veg, same type of calculations used to determine PPFD for the tasty lamps. I was very happy with the veg rate under that lamp. It's not something I would suggest flowering under in a 3x3 but it would do a great job of vegging. I've actually veg/flowered in a 3x3 using a PPFD of 500 through the whole grow. Not bad results GPW wise but lower wattage = lower yield.
It was
@OneHitDone that flowered under 242 PPFD. I assume the plants were vegged under similar conditions. Veg doesn't take a lot. That's why CFL panel intensity produces similar veg times to higher light levels. Before my LED switch I was using 2x4 and 2x2 8 bulb panels in a 3x6 area. Fantastic veg times, yield not so great.
I had a 2 cob nominal Vero 18 gen 5 lamp in an 18x36 cabinet I used for mom and clones, 60w output at about 35% efficiency, about 250 PPFD. Worked fine.