Feedback on the meaning of: sea_ice_area_fraction_of_sea_area_fraction

I wonder if it might be possible to provide more description on the: `sea_ice_area_fraction_of_sea_area_fraction` variable. The reason I’m asking is that it has generated quite a few questions. First let me provide the description of the variables used by the Met Office:

1. The fraction of the wet part of the cell that contains ice. Some cells are part land and part water (along the coast for example). This variable is used in our atmospheric DA and we include all water bodies so lakes are included for example.
2. The fraction of the cell that contains ice. This is used by ocean DA and from what I understand, the model cells do not contain a land part.

Does anyone know how `sea_ice_area_fraction_of_sea_area_fraction` fits with these descriptions?