IMD should be expressed referencing a single tone of a two tone test
signal. That is the way most tube manufacturers do it.

Some of the radio manufacturers reference IMD to PEP which makes it
look like the IMD is 6 db further down!

The PEP of a transmitter is 6 db higher than either tone of a two tone
signal.
If the IMD is 30 db below the level of one tone of a two tone signal
then it will be 36 db below PEP.

73
Gary K4FMX

Poorly expressed on my part. Thanks for the correction.

W4ZCB