When we try to “calculate” coverage we base it on how important it is to hit the mark. Fertility has the luxury of being able to move around the tree once applied, but one still needs to maximize the coverage. When we spray gibberelic acid for cherries (very location dependent) we always do a higher application rate (150 gallons per acre vs a normal 100 gallons) and bump the material rate up maybe 20% due to the extra loss. Speed is actually more important in terms of coverage than volume, lots of studies show that going too fast makes you lose coverage. We aim for 2.0 mph on our 20′ tree rows, and 2.5 on our tighter blocks at 16′. You also need to remember that really you are applying a material amount per acre, just like if it was a nitrogen application to the soil. If you did (for example) 10 lbs of potassium nitrate per acre some might say the concentration matters, but the end result is you applied 10 lbs. Some might say a higher concentration will go in the leaf better, but that concentration will change over time as the water portion evaporates, so you will eventually (and quickly) have a more concentrated spray drop on the leaf surface. You could also say that a higher volume would spread the material out more and you would have less burn in those more highly concentrated areas of spray coverage, which is fair. The end result is get the best coverage you can, with a concentration that won’t burn your tree, and don’t worry so much for a rate rather than an amount.