Note: The USB MOD Level (Menu 39 of IC-7410) is set to 100%, and the RF output power level is minimum (around 1 watt) in all the following cases.
The output volume of Linux sound system is far bellow the maximum.
WSJT-X Transmitter Audio Leve: -30dB.
WSJT-X Transmitter Audio Leve: -20dB.
WSJT-X Transmitter Audio Leve: -10dB.
WSJT-X Transmitter Audio Leve: -6dB.
WSJT-X Transmitter Audio Leve: -3dB.
WSJT-X Transmitter Audio Leve: -1dB.
WSJT-X Transmitter Audio Leve: 0dB.
It seems that the signal suffers from some clipping when the Transmitter Audio Level is set to 0dB.
From the top, the Transmitter Audio Levels are; 0dB, -1dB, -3dB, -6dB, -10dB, -20dB, -30dB, -40dB, and -45dB.