Chungjh has a good point. You should be measuring across the variable pot. My reaction is that 1.6 ohms seems low. If that’s the correct measured value, I would only say that a fixed resistor will sound cleaner and more open that the measured equivalent on the variable pot. For a small cost, I might suggest you buy a few values, 4 and 3 ohms( 50 watt, non conductive) and the 4 ohm a try. If you want more treble, then consider to go down to a 3 ohm and solder that value in place.
Good luck, I do look forward to your
Feedback on the treble sound change.
The test looks ok. Your call on inserting the resistor load. Again, my experience is that a new fixed resistor will sound more extended, and cleaner, than the pot, so you may not need to lower the R value down to less than 2 ohms to get your preferred HF extension. Not sure I would…