spam cutoff less than neutral?

[Tom Anderson]

robx=0.455
robs=0.1
min_dev=0.25
spam_cutoff=0.55
ham_cutoff=0.15

I'm receiving zero false positives (awesome).  I receive on average
maybe one false negative per day (pretty good).  Upwards of 60 spams are
successfully classified (nice).  But, I get 20-30 unsures which are
almost always (>99%) spam.  I use -u, and correct all errors and
unsures.  Many unsures are of the type I previously identified on this
list... they are very long and contain many normal English words,
generally scoring 0.5 and not moving much from that after repeated
training.

Given these numbers, I'm tempted to move my spam_cutoff even further
down.  However, since 0.5 should theoretically be "unsure", I'm hesitant
to move the spam_cutoff much further due to the philosophical
implications.  This is particularly true if I move spam_cutoff too close
to robx.  False positives are unacceptable, and heretofore unseen emails
need the benefit of the doubt.  Already my spam_cutoff is less than
min_dev, which itself seems somewhat hypocritical.

Should I keep my spam_cutoff as is and just continue correcting
unsures?  Or is it safe to move it into "unsure" territory?  Does anyone
else have a very low spam_cutoff?  Does it produce any false positives? 
Can tweaking the other numbers push more of these unsures into the spam
territory without moving spam_cutoff?

Tom

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