FOG Index scores for EFL students

Does anyone out there know what an appropriate Fog Index (and/or Lexical Density) would be for text designed for EFL students at Cambridge Pre-Intermediate, Intermediate and Post-Intermediate (Pre-Advanced)?

I teach in the rural areas in Saudi Arabia where English is rarely heard, and westerners rarely seen. I really am desperate to get some idea of what I could justifiably expect, in terms of the experience others have with this kind of text analysis.

Please accept my thanks in advance for your time and advice in reply to my appeal for help.

Salem bin Daoud
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