Yeop, so when you cut the centre divider, just make sure it is measured up and you cut it so NO air can escape through any holes through/before it hits the filters.
Best way to know if you've done a good cut, is put the filters in, and if they are a snug and little hard to push in -- you've got a pretty tight fit.
As for whether there _IS_ a hard plastic divider part in the centre of the filters -- I am not totally sure perhaps some of the cabin filters do.
I think the cabin filter I purchased, it wasn't precisely in line. BUT , you can be sure it does a good job seperating the two sections anyway as it is just another 20mm of added plastic tbh and I'm sure its still going through the filter paper->though to the other side all the same. Mines works as normal, definitely has gotten rid of all the mould/harsh bacteria smells. I kid you not, I used to cough while driving... breathing in the s*** stuck in the original evap box. But I have renewed the entire system minus the lines and 2 AC control relays for the low speed controls -- so there should not be any smell at all !
Compressor, Condenser, Evaporator, TX Valve, Blower, blower resistor, all sensors (thermister/AC temp sensor), comp oil, orings + regas'd at the shop. Brand new AC system in effect. Anyway, I can't live without AC and I love my 105 so job was definitely worth it

Can't wait for summer, dont need a fan on the condenser at all but might buy the 100 series fan online and slap it on just for quicker cooling temps on those hot days!