[Elecraft] L1 vs W1 Power Reading

[akiwi ham]

I recently put together a DL1 dummy load and W1 wattmeter.

I have the DL1 connected to my KX1 through the W1. I have the W1 connected
to a computer using the W1 software. I have a significant difference between
the power reading from the W1 and the power calculated from the voltage
measured on TP1 of the DL1 using a digital volt meter.

For example:

W1 reading = 4.04W

TP1 volts on DL1 = 8.97V => 3.29W

Is this magnitude of difference to be expected?

Bryan, Zl1NI