Right now your ROE is capped at whatever the market rises.

Thus, my ROE slowly gets worse and worse and once I drop below 10% ROE that is my signal to re leverage my equity, to keep it working hard for me.This feels long winded and possibly not all that intelligable. 

@Max BrunkeThank you for heads up, but my current situation qualifies for the "only one Dwelling Unit in the City of Portland" exception.Hopefully the bill in Salem that would allow municipal rent control dies, and this Portland ordinance gets overturned.

Again your ROE is currently ~1.84%, it’s like a fat slob sitting on the couch.  

You also mentioned duplex equity though your ROI may be different from your return on equity (ROE).

I agree with @David Roe in respect to the due on sale clause. 

If acquiring a new rental could be 10% or 20% ROE on your cash, consider doing that, instead of earning 4 or 5% yield on your money (by prepaying the 4% to 5% APR loan).Only you can decide how much risk/reward you see in the leverage, and what's right for you.

What is a legal way for both of us to benefit from the ROE while still getting the mortgage in my name for the FHA?

This might be overturned if its not a "hot" area and with number 1.

No leverage equals a lower ROE, less risk, and more safety margin.