I don't have any privs here, but here's my general thoughts on the question
How many active reviewers are there?
If there's not a lot of active reviewers, that's a good reason to lower the threshold. The close review stats page seems to indicate there's not a lot of reviewing going on. The fact that there's two moderators in the top 10 also doesn't bode well (it typically means that moderators are cleaning out the queues because the community isn't voting enough).
How many close votes age away?
A problem I noticed on DIY.SE was that a lot of votes weren't being done to completion. A lot of times, it was due to votes aging away. If this is a persistent problem, it means the voting culture needs some help.
Is closure timely?
A major reason we close questions is so you don't wind up with terrible questions you can't get rid of. Once a question gets answers, it often starts garnering upvotes and the whole process breaks down.