Tank gear has equally high amounts p.def and m.def. Pseudo-heavy armor, such as scalemail for lancer, have medium amounts of p.def and low m.def. Caster gear has low p.def and medium m.def. It can be very confusing early on, but if you are tanking, only look for armor wearable by marauder or gladiator only. Any armor usable by lancer will be more skewed towards p.def.