[phenixbb] Mask used for map-to-model FSC

Hi all, Does anyone happen to know how to control the tightness of a mask for map-to-model FSC calculation? I have tried the "atom radius" in Map/Model CC tab of "Comprehensive validation (cryo-EM)", but it was not working for me. The reason I am asking this question is that I can only model a small region in the cryoEM map, the rest is unknown to me. Then the CC in low-frequency was 0.4-0.6 in the FSC curve, while the overall masked cc was 0.85. I would like to find an easy way to make the FSC curve look better. Any suggestions would be appreciated! Best wishes, Yang