1200 Mbps is a theoretical value for a very pure environment. In reality, the circuit line in a house is not pure as it has noise from other devices such as TV, refrigerator, microwave, or other electric appliances, which affects the circuit environment.
Besides, the circuit signal will be attenuated when transferred to different nodes/power sockets. Therefore, if you put the device in another environment, the physical rate will be based on the quality of the current circuit environment.
The factors for impacting the network environment include: distance, network traffic, and noise on electrical wires, quality of electrical installation, and other adverse conditions. The rate obtained at the application layer will be much lower than the physical layer rate (the 2 PLA devices’ physical rate, not data rate).
You can check the physical rate (PLA===Electrical===PLA) in the PLA's utility.