What is the GS standard for distinguishing battlefields?

What is the GS standard for distinguishing battlefields?

It's not one specific value?

It changes depending on amount of players queuing BG's.

Its just a personal guess, but i believe you got 3 gear brackets.
You got Low bracket - up to ~4.5
You got medium bracket - ~4.5 to ~5.8
You got high bracket ~5.8 and above.

I've seen low-med games, i've seen med-high .but didn't once played in a low-high.