Just how shade tolerant is supina bluegrass? A pondering of an experiment

So I think I've seen that supina bluegrass is quite shade tolerant, but I was doing some wondering today as I watched our irrigation system water the weeds out under the trees (perhaps years ago there used to be grass out there when the trees were smaller?): just how much shade can supina tolerate? Our backyard has numerous mature trees, and thus lots of shade. The lawn we do have back there gets some mid-day sun due to some clearing provided by our deck and the trees being further from our house.

Left side

Center

Right side

I am quite certain that we could extend our lawn further under the tree canopy. In the morning as the sun comes up over our house the light shines back under the trees since the lower limbs have been removed up to probably 15-20 feet. The question is just how far into the shade zone can the supina bluegrass tolerate?

There would be some benefits if it could grow there:

1. Obviously more awesome grass to look at, walk, run, and sleep on (duh)
2. Potentially better protection from erosion during heavy rains
3. It would help keep weeds from growing there which I continually have to fight
4. The irrigation system already reaches out there, so no adjustments would need to made

Hmmmmmmm...