water levels

[Bob Siedel]

Hey everyone, 

If I was trying to maximize grow area, and minimize FT area, would I be wrong in assuming you can calculate water volumes by taking water height in GB x width x length to get a more exact cubic foot, x 7.5 to get gallons, x 0.6 for media to get ST volume, and then dividing this number to get the FT volume or (GB x 7.5) / 2 = FT?

ex.

10/12" x 6' x 2' = 10 cubic ft x 7.5 = 75 gallons x .6 = 45 gallon ST / 2 = 22.5 gallon FT or 75 / 2 = 37.5 gallons

as compared to 

6' x 2' = 12 square ft x 7.5 = 90 gallons x .6 = 54 g ST /2 = 27 gallon FT or 45 gallon FT

I know more water is better and mature systems can be taken up to a 3:1 ratio, but I'll probably only have fish as pets, and I want to make sure I have enough FT volume to control the number of fish in case the plants need more nutes while still bringing this volume down as much as I can.

Any ideas on this is greatly appreciated, thanks