Oct 7View SourceYou do not indicate what "sound card" you are using.
Many sound cards will not drive the softrocks to full output.
Some can easily overdrive them.
Look at the RMS voltage being applied to the SR input.
Should absolute max out at 2V RMS average 1V RMS.
Many power meters are not accurate at low power levels
and wide band transmissions will show lower power than CW.
SSB about 1/2 of CW for most.
Regards 73 Eric VK5ZAG