Not really sure I'm following when u say:
Vegging at around 20" away for 18hrs at 400 umols/s/m2 gives a DLI of ~ 25
Full flowering at 12 - 14" away for 12hrs at 800 umols/s/m2 gives a DLI ~ 35
Using the MH TS600 PAR Maps for reference.
I would veg the plant with that fixture at approximately 20 inches away for a period of 18hrs of light, 6hrs of darkness.
In Flower 12- 14 inches away, 12hrs on 12 hrs off.
That's what I do anyway.......
Don't be worrying about the DLI - Daily Light Integeral
Where PPFD expresses light intensity in a second, DLI expresses the sum of those measurements in a 24 hour period (86,400 seconds per 24 hours).
Just I noticed DLI mentioned previously In the thread so I calculated the DLI from the par map of the Mars light.
Here's a handy DLI calculator for any nerds interested ....
With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.
www.waveformlighting.com
Waveform also have some other decent calculators too.
Lux to par, lumens to ppf, etc