Okay, new idea.
I think I'm going to put all my shrimp into the main tank, and have the puffer in a planted, 5gal tank. Yay.
From experience, the lone DPs are more relaxed and more funny to watch, especially males . A planted 5gal will be perfect. You can leave a few adult shrimps in there. I've been keeping cherries and DPs together for the last few months and they have been fine so far. No antennae or leg nipping, YET . Obviously shrimp babies get eaten but some still survive.