Thank you for posting this. I will be doing some testing tomorrow. I draw a new layout with the help of your diagram. I have added a function switch, too, to recall a preset I will associate with the expression. I have seen pictures of the internals of Mission SP-H9; it has a resistor somewhere in the circuit. I hope it’s unnecessary, and the diagram below will work just fine.
With all fairness, I’m a bit disappointed with Eventide. I asked the same question via email, and the diagram for EXP was refused to me. I would understand if Eventide sells an EXP/SW pedal dedicated to H90, but now I have an expensive unit with no info on an actual spec for the expression pedal.