Attic insulation measuring 6" less than original install

[Dixon.plug]

The original insulation was installed in 2008 and the contractor documented 16 inches of blown cellulose at installation, which should have been R 60. Just measured depth across the attic and I'm consistently seeing 10 to 11 inches, hat's nearly 40% loss from settling over 17 years. Nobody has been in the attic disturbing it, so there should be no moisture issues, no compression from stored items, just gravity doing its thing over time which is fine
Is this level of settling typical for cellulose? I've read 20% is expected but this seems excessive

 

[furg0y]

40% is high but not unheard of for cellulose over 17 years, especially if it was installed at lower density, the 20% rule is more for dense pack applications