OK, on the setup, but just one thing I am not clear on. You say the metering is on the supply to your custom board, What functions are on that board?
Amtel uP, level converters,SI5351A?
I want to make sure I meter the same components.
Yes I agree that KE1L suggestions need investigated. Especially in the area of I2C level conversion/communications. The SI5351 can be set up with just a few register transfers, or a continuous stream of redundant commands that just waste energy. Those redundant commands can cause havoc on the SI output signal.