Hard to block 2 Trog armor rolls a 5 as the final number. Unless he can roll a seven, I don't understand how he gets a five.
Armor (grey cards) are not affected by hard to block, it only affects block (green cards). Hope that helps make it a bit more clear. (if you want something to bypass armor, look for penetrating attacks)
Hard to Block only affects Block cards (green border) not Armor (grey border). It doesn't help that Crude Plates is one of the few Armors that only trigger from the front like Blocks normally do.
More accurately: "This armor doesn't prevent damage from attacks behind you. If this Armor prevents damage, move back 1. " It blocks terrian damage.