What matters is the TRX power at BTS output.
Between the TRX and the BTS output, there are some combiners (ANCs, ANYs), as many as you need.
Each of them will drop the TX PWR by 4dB (approx).
In case of 4 TRX, only one ANC. So each TRX losses about 4dB.
At BTS output, the weakest TRXs are the TRX2, 3 and 4. So the TRX1 will be attenuated so it doesn’t exceed the output power of the 3 other TRXs.
That is for GMSK only.
IN 8PSK, the TRX1 will send the max power, and so does the other TRX2,3,4. But of course, Tx Pwr 8PSK in TRX1 is stronger than in the 3 others. But here, there is no levelling. The TRX1 is not attenuated in 8PSK.
I hope it is clear now. If not, I’ll just blow my own head off.