I tried what you are trying to do (e.g. try to make your standard tuned guitar sound like a dropped tuning) with Polyphony and I got the same results. The H90 is brilliant and constantly amazes me but this is one thing that, in my opinion anyway, it can’t do. That doesn’t mean it’s any worse than other pedal attempts from other manufacturers. I’ve tried a few.
I suspect you would better achieve this with modelling (e.g. Variax or Boss SY1000).
I’m sure we are going to get better Poly algorithms in the future but whether this is realistic or not is another matter.
