9 months later...
In case anyone is interested, after 9 months of this experiment I found a few things:
1- A mini-jet 606 isn't quite powerful enough to effectively run this reactor this way.
2- Dividing the media into two segments within the reactor is not really worthwhile. There doesn't seem to be any real advantage over just letting it all mix together, and fluidization and flow are much better when all the media is allowed to freely mix and circulate within the reactor together.
In retrospect I would just purchase a two-stage reactor from BulkReefSupply.com if I had to do it over again. In fact, that may end up being what I do when it comes time to replace the media I have in the reactor now. BRS reactors have better design and build quality than the Two Little Fishes Phosban Reactor 150, and I like the ease of their cartridges.
55 gallon reef tank. AquaticLife 4-bulb T5 HO with 4 LED moonlights. Reef Octopus BH-1000 HOB protein skimmer. TLF Phosban Reactor 150 running 400ml of NPX Bioplastics with a Maxi-Jet 1100 and a BRS Reactor running activated carbon with a Maxi-Jet 900. Vortech MP10w.