It's not listing Steel Fiber as a 1.1x modifier. The additional armor that Frost gains from equipped mods is what's factored in the health expression and not Frost's total armor. Since Steel Fiber is a +110% base armor bonus, "1.1" goes into the expression.
Check the abilities menu and experiment with different amounts of armor on Frost. The health expression in Snow Globe's article should make sense.
With +90% base armor equipped, you'd be still be adding to Snow Globe's base health. 5000 health unmodified compared to 6350 health modified is a net increase in health. Also, Snow Globe's health is not related to its size. That's where power range mods come into play.