Subject: what causes nitrogen to be different than oxygen/carbon (atomic radius)?

I submitted a question previously about why Nitrogen's atomic radius is lower 
than both Oxygen's and Carbon's radius.  I checked the archives and all I could 
find out was that radii tend to be larger as with the higher shells and from 
right to left.  What I don't understand is that from Boron to Neon this pattern 
holds good except at Nitrogen.  Nitrogen's radius is smaller than both Carbon 
and Oxygen.  Why is Nitrogen an "oddball" compared to its neighbors on the 
periodic table?  Why doesn't its outer unpaired electron repell other electrons 
thus being less stable and therefore having a higher radius?

Re: what causes nitrogen to be different than oxygen/carbon (atomic radius)?