OP, RX and UPR are both good units, plenty of YouTube videos on installation that you can copy. The RX site has both YouTube links and an actual diagram to follow if you want to replicate.
As for the RX can catching what the UPR missed, I'd chalk that up to probably neither being capable of catching 100% of anything and the RX being downstream of the UPR there's some additional cool down and condensation available.
I look at it like the large IR air compressor at work. It has a series of tubing, fins, and a fan to cool down the compressed air and let moisture condense to the drain. Then we have a second air conditioned dryer further down to really cool the air and take out the remaining moisture.
It's just my opinion, that having time to cool the blow by gasses to condense is probably one of the most important factors, so length of hose and placement of the can should be a big consideration.
You didn’t read. It was tested with the RX downstream and the RX caught 4x the fluid. They were then switched and the RX caught 19x the UPR (95%/5%). The UPR was then upgraded and put back in front and there was still just as much in the RX as there was in the UPR indicating even the upgraded UPR caught 1/2 of the contaminants passing through it at best.

