I emailed specialized about 2.8 and they said they would not fit
The manufacturers always take their safety margins with mud clearances and rims/tires being out of true. (though I do admit rear clearance is not big as it is)
Got the same negative answer from my previous bike's manufacturer - max tire is 2.4.
after some measurements taken by me - installed a 2.8 that fits in there easily, ridden it like that for 2 years without issues, other than tight mud clearance, but that is never an issue here.
So if it fits properly, and someone already has positive experience with it - I'd give it a go.
@daju - can you please confirm R-2.8/F-3.0 size tires refers to a 29'' rims on the 2019 LEVO?