Update: I just finished playing around with the carrier point adjustments, listening through the 1.8 filter. I ended up with both USB and LSB set to -180. I arrived at that by listening through the 1.8 filter on USB and adjusting the USB point until it sounded right. Now, I can switch from the 2.7 to 1.8 filter on USB without a change in fidelity - a big improvement!