I think I've seen my 2490 down in the .14 territory for 0% backlight black levels, FWIW.
LCD backlights get weaker over time. How many hours on yours?
My 2490 at 0% was like .25 (166 white) when new, now it is near .20 (140 white), Probably .15 (110) in another year or so.
The really seem to drop pretty quick as the hours accumulate. I really should shut mine off more when not really using it.