This is the actual maximum transmit power ceiling for the tone identified by cvdslMCMConfProfileMaxTxPSDTone, expressed in the same 0.5dB steps off the -140dBm/Hz reference as the target PSD table, but functioning as a hard upper bound rather than a target. It's the enforcement mechanism that keeps this line's transmitter from exceeding regulatory limits at sensitive frequencies even under adaptive power algorithms that might otherwise push power higher to compensate for a noisy line. A very low ceiling value at a specific tone, well below neighboring tones' ceilings, indicates that frequency is under strict regulatory protection, such as an amateur radio band notch mandated by spectrum compatibility rules.