Having had many long conversations with HP on this my understanding is that there is a 'feature' (bug) in later IMC versions that overwrites the Cage setting when ever you edit/create a CPG with Port. From what they've explained on a T/V class (because the trays aren't chained) Port=Cage (mostly) so not to worry...
I got lots of blank virtual stares and repeats of the Port is better then Cage or Port=Cage when I pointed out that we also run a F class were the trays are chained so Port is not the same as Cage for us.
The trick is to use the CLI to create your CPGs and avoid saving any changes to them in IMC, you should then actually get Cage when you write data to the VV in that CPG.
I've yet to get to the bottom of why this 'feature' was introduced and why it's still there after I'm sure plenty of others pointing it out to them. From what I gather there might be a new version IMC released in November with 3.1.1mu3, I look forward to testing this again at that point.