ORIGINAL: m10bob
Kinda late to weigh in here, but this site pretty much justifies Bill's comments ref the Bell P 63 as a ground support plane,(designed as such from the "gitgo"), and that while armor WAS increased for it, the new engine WAS more powerful than its' earlier predecessors..
http://www.aviation-history.com/bell/p63.html
As noted above, its true that it had more armor compared to P-39s. However, still less than many armor: 1 aircraft in the game, so it IMHO should not get the rating but just a bit more durability. P-63's armor could not provide nowhere comparable level of protection that Il-2, Il-10, Hs 129 or even Fw 190 A-8/R8 Rammbock's armor could.