Hi mutt,
All engines, bearing in mind that the acceleration to clean speed and clean up will be accomplished somewhat before 20 to 30 miles, but the crossover point occurring later, about 20 to 30 miles out.
All 'finger in the wind, a guesstimate for day to day observations - no rocket science. With OEI, 20 to 30 miles would only represent the point where 4th segment began.
Regards,
Old Smokey