Regarding crit, as I said it indeed acts in favors of the +Weapon Damage.
Regarding Opportunity, it's what makes the 150% multiplier from Backstab become 180% (150 * 120% = 180). Unless I'm mistaken, Opportunity changes the multiplier but doesn't affect the flat 225 Damage of Backstab (and it's the same for Ambush), Opportunity isn't *really* a +20% to Ambush / BS damage.
1.7 is indeed the normalized coefficient of AP contribution for Daggers.
