Ah, and an age-old question you pose.....
EPA guidelines for most herbicide registrations require that the use-rate be stated by "area" rather than "concentration". Therefore, many products will list a rate per-acre or per acre-foot of water rather than as a mixture-ratio.
Enter the term "calibration"; which is exactly what you alluded to in one of your earlier paragraphs.
In many cases, the dilution ratio in your mix tank is of less concern than the amount of actual product being applied to a specific area.
EX: When treating a 1-acre pond, there's virtually no difference between mixing 2 gallons of product XYZ into 10 gallons of water and applying that mixture to the 1-acre pond vs. mixing 2 gallons of XYZ into 20 gallons of water and applying that mixture to the 1-acre pond. Either way, you applied 2 gallon of XYZ to the 1-acre pond. Only your water-volume (carrier) was altered.
So, you're right on track with your earlier "question". Figure out how much water-volume (5 batches) you'll need to complete a treatment to a known area-size (1 acre). Then, add/split the specified amount of product (2 gal) to treat that area (1 acre) into the pre-determined amount of water-volume (5 batches).
When depth comes into play (as with CUTRINE), you simply multiply the acre-foot rate by the avg depth within the treatment area, while using the same application-volume concept discussed above.