Increased Lightning Damage on Staff questions

I see there are two Increased Lighting Damage mods on a 2H staff. Do both of them increase Spell damage or only one of them is? Which one? Prefix or Suffix?

The one in prefix increases up to over 100% Lightning damage and suffix is only up to 30%.

both of them will affect lightning dmg of spells

Oh wow.. that's cool. Just the suffix is a lot weaker! Got it.

I find it strange that Staff has very low critical mods on it. It's the same as 1H weapon. Why is that? 36^ critical damage is the same as a Wand. That seems very odd to me.