Meter war !

[KK2DOG]

No Bird 43 here so take it for what it's worth. I'm running FT8 with an amp and got the following readings:
LDG AT-600Pro Autotuner 200 watts
Diawa CN-801 HP 275 watts
Palstar PM2000 250 watts

All meters are in-line and are 1,2,3 in the sequence.

 

[RFI-EMI-GUY]

Try a CW unmodulated carrier

 

[K4EET]

200 plus watts for FT8? Wow!

But yes, terminate into a dummy load and put your rig into the "tune" position. Make the readings there. Then do what RFI-EMI-GUY said. Again, make the readings at the 200 watt level. Finally, crank up the power to maximum (if the dummy load can handle it) and make the readings again. With a set of readings like that, we can better see what may be at play here.

73, Dave K4EET