The value calculated in https://github.com/elastic/beats/blob/master/metricbeat/module/system/diskio/diskstat_linux_test.go line 88 does not align with the documentation:
The average size (in sectors) of the requests that were issued to the device.
Diskio metricset calculates bytes and does not simply pull the sectors value from iostat. The documentation needs to be updated to say bytes instead of sectors.
I accidentally created a github issue before posting here: https://github.com/elastic/beats/issues/14204