So I ended up doing a solo run on the defence mission in order to get the scans I was missing (still missing 2 flameblades, 3 brunts and then I'll ignore eximus reavers)

And I was incredibly surprised when an enemy reaver ended up giving me Iron Phoenix. It was the only mod drop throughout the entire mission (none of the kavat's were feeling generous), but I've got no idea if they actually are meant to drop them or not.

Anyone else got non-kavat mods?

(Given that on enemies that do drop iron phoenix, it's at an incredibly low chance, they might have just tranferred hellion's drop tables and taken everything else off, but other than that I've got no idea how it ended up dropping)

I'll put a screenshot when I get the chance.