Mithral Full plate fortification

[Hogeyhead]

Can you put heavy fortification on a set of mithral full plate, or only moderate?

[Arkat]

You can put Heavy Fort on any sort of armor, Light, Medium, or Heavy.

It's a +5 bonus no matter what you put it on, though.

[Azothath]

on AoN → Fortification(heavy) falls under magic items.
There is no mention of armor type, category, or special materials.