I think the loss of higher frequencies as you lower the trim is in your head (or more specifically, your ears). This is a digital trim which does not cause treble bleed; it's not like reducing the volume using the volume knob on your guitar. It's like putting a null filter in front of the amp which just decreases the signal level. Of course if it affects the volume of the patch (which it will probably do to a great extent with such low breakup), then your ears will play tricks with you, since your hearing is not sensitive to high frequencies at low volumes. Once you turn down the trim, turn up the amp level to make sure you're getting the same volume as before, and the highs should be there.