This is actually two issues...   the main problem I have is that right before a layer change, and before combing to the new location, the Z height changes. This makes combing useless, as there is nothing to comb against, so the result is stringing. Z-hop is disabled. It doesn't matter which combing mode I choose--the result is always the same.   Previous layer's infill finishes; Z goes up; it "combs" to the start of the next layer; next layer's wall begins printing.