what i think the op was saying is that
when you cast molten armor, it takes whatever you spirit you have at that moment and convert it to crit,
so by switching gear and set bonus, you can "cheat" and gain a little bit more crit
i did a quick test in dal:
my initial fire set was
1246 crit, with 358 spirit
after switching a 2pc t9 and a few spirit gear,
1228 crit, with 675 spirit (2pc t9)
then i switch back to my inital gear, i have now
1300 crit with 358 spirit again
when i recast molten armor with the inital set,
the number goes back down to 1246
so, my conclusion is, it works
i guess i gain like 54 crit out of it? /cheer