Critical Kills - with a Bishop ! errr? .. pls explain this...

[Mr Creosote]

I have a lev 13 Elf Bishop with 3, yes 3... in Staff and Wands, 2 in close combat and no other points in melee type skills, she has game starting attributes in everything except INT and PIE and a couple of extra VIT.I equipped her with the Staff of Doom when I found it. She uses spells of course most of the time but occassionally gets to swing the Staff of Doom, and she crits about a third of the time (the staff attributes show a kill of 15%).
My Lev 14 Ranger has Senses maxed, decent STR, DEX, SPD etc etc
Bow at 100+, Mod weapons 40, Ranged at about 80, Eagle Eye about 10, plus extra from the Bela bow when I am using it. I have used the bow from Bela, also Blunderbuss and Seige Arbelest on her. Ammo is musket balls when using Blunderbuss, Barbed arrows, and I can't recall the name of the bolts, the ones slightly better than the basis that are generally available. She crits about 5% of the time.
So..... how come I have a Ranger with great stats, almost the best weapons (I realise not the best ammo but thats not really available to me yet), and yet she is totally pathetic in combat crits compared to a Bishop with low stats and a good weapon.
I used a Ranger primarilly for ranged crits and its not working. From what I am experiencing in my game I feel there must be another that determines crits other than the "published" attributes. Any ideas? I'd like to improve my Ranger.