efficiency of any cyclone will depends upon the particle size and the entry velocity basically.

entry velocity will change if the temperture changes(because volume changes with temperture)

also the particle size is very important, In cement laboratory people check retaintion in 212 , 90 and 45 microns . but the lower fraction of particle size very considerably on a VRM or ball mill for same feed rate and same separator condition.

the top stage cyclone efficiency is checked by checking the dust load at inlet of Ph fan.

Also the feed factor depends on the tyoe of fuel being used.

IF we use coal the ash will be absorbed with clinker and factor will be little less, based on ash content. If oil/gas firign is used, then no ash absorbtion and factor will be little higher.