Should we set the boom height for the top of the canopy, or how do boom height and canopy relate when applying fungicides?

You should spray for correct nozzle tip overlap at the top leaf canopy, otherwise you will get streaked application in the top of the soybean plants. Boom height should be measured from the top of the soybean plant canopy during application.

An exception would be if the soybean canopy is not closed and you are using drop nozzles inserted between the rows. – Mark Hanna