IPS in general gives me a headache, but I can usually work it out with some coffee to help. Your system looks like your chainring affects only your gearing. The Stokers chainring affects both of yours' gears. Pretty similar to the way it is on 'conventional' tandem drive-trains. On your system your 'timing rings' are not independent. It gets to be a mess changing things around. But since you aren't in a fixed Captain/Stoker link it could probably work.
I'll admit a bias against IPS, even simple systems like on the Terratrike. That said, shortening your cranks with crank shorteners allows you to preserve IPS on your trike. I don't know if you can get to the 130's but at least into the 140's. I don't think it's worth it to do more. I wouldn't, however, argue strenuously against getting some conventional used cranks from a bike co-op and forego IPS altogether. Has it been your experience that your cadence increases when/if you shorten your cranks and/or lower the gearing? I personally don't think it does. What I see is that your cadence stays the same and you go slower. And that's fine. But if you ride with others it may start to seem like you are always chasing them.