So I have a Rogue Acrobat / Monk that I am leveling. Currently Rogue 9 and Monk 6. I took Tier5 enhancement Staff Specialization (from Thief-Acrobat tree) and at level 15 I took Improved Critical Bludgeoning in order to get 18-20 critical range, at least that was the plan. I equip my different staves and all I get is 19-20 …

Am I doing something wrong?
Do they not stack?
Should I visit Fred and get something more useful than IC

Help please