I used to be a Tire Engineer for Dunlop, and all my experience deals with passenger car radials (not trailer tires). However...
I do not see any reason to inflate tires above the maximum pressure unless they are overloaded. And they should never be overloaded, because that means your trailer is overloaded. If they are overloaded, you can overinflate a bit, but I would not go more than 20 psi over the stated maximum cold tire pressure. Remember that the pressure goes up anyway as the tire warms up running down the road.
Underinflation is the worst thing you can do to a tire. Underinflation causes heat generation, which will destroy the tire, especially at high speeds, high loads, and hot weather.
The reason why I say no need to overinflate is that the maximum loads are conservative. I don't know if we ever had a tire to fail the DOT load test in the 5 years I worked for Dunlop. We often ran them to failure in the high speed test, but the load test was essentially a legal formality. The tires never failed it.
However, I cannot speak to how things are done in China.