Using an envelope or a mask to start phasing even with high NCS is still worse than using a low res model from cryoEM that is characterized by an (almost) proper density distribution.
One has to measure the intensities of the very low res reflections (0 0 1 and the likes) precisely. The presence of high NCS does not guarantee a success even if your initial model is "good" as described in Section 9 here: http://www.ncbi.nlm.nih.gov/pubmed/11526317 Petr ------------------ Petr Leiman EPFL IPSB-LBBS BSP-415 CH-1015 Lausanne Suisse
