Basic math shows that 256km x 256km would be tight going edge to edge (and they are never truly edge to edge)
An aircraft traveling mach 1.5 (not exactly hard these days) would only take 8 minutes to go edge to edge (256km distance)
Assuming an aircraft does the same in the other direction. Then thats only 4 minutes to pass each other. Let alone release weapons. About 3 minutes 30 by my reckoning for both sides to get and fire a 40km AMRAAM shot at each other.
Though diaganol angles do help a lot (362.04km from corner to corner)
That’s not a real thing though, it’s just used to describe nations that have more content than others.
When it comes to modern air China very much is a major nation competing with the US and once we pass into 5th gen even surpassing Russia in what there is to add.
To be honest I don’t understand why they don’t focus more on the simulator mode, with a little more effort it would become the best aviation simulation game, well ahead of its competitors