[phenixbb] B-iso vs. B-aniso

[Yuri]

Dear community,

The protein model I am refining has 400 amino acids (3320 atoms).
Some real quick calculations tell me that to properly refine it 
anisotropically, I would need 119,520 observations. Given my unit-cell 
dimension and space-group it is equivalent to about a 1.24 A complete 
data set.
However, I have had a couple of cases where anisotropic B-factor 
refinement significantly improved R-work and R-free, while maintaining a 
reasonable R-gap, for lower resolution models (1.4-1.5 A, around 70,000 
reflections). What is the proper way of modelling the B-factors?
Any thoughts/opinions/call-outs from the community are welcome.
Cheers,
-- 
Yuri Pompeu