Hello,

The Program mix works in a way that reduces the volume of either signal. At 0, the wet mix is reduced completely, at 100 the dry signal is reduced completely. At 50% both the wet and dry mixes are not reduced at all, so both signals are at full volume, and this can result in a perceived increase in loudness.

If you are using Kill Dry, the mix knob becomes a level control for the wet signal. There is no dry signal to blend, the mix knob is simply a level control for how loud you want the wet signal. I would suggest continuing to use Kill Dry for whatever effects are in the loop of the amp and use the mix control for that preset to adjust the wet signal to test. Your level for a wet signal may be different for reverb or delay, for example.

Does the amp have a mix or level control for the effects send? Have you tried running the H90 at instrument level instead? The FX Loop of the amp is most likely a line level signal but your path before the preamp could be run at instrument level.

Bypass mode should not make a different when settings your levels.

Let me know if that is helpful.