I'm having trouble creating a formula to tell me an accurate tank volume in a tank when it is tilted.

I know the following:

Step 1: Tank Capacity

Tank Diameter:96 inch
Tank Length: 256 inch

So total capacity is : 8021.59 Gallons

Formula [=(("Diameter"/2)*("Diameter"/2)*PI()*"Tank Length")/231]

Step 2: Tank Volume measurement using a dipstick

Striker plate: .25 inch
Stick Reading:78.75 inch

Volume in Tank:7,062.54 Gallons

Formula [="Tank Length"*((("Diameter"/2)^2*(ACOS((("Diameter"/2)-("Stick Reading"+"Striker plate"))/("Diameter"/2))))-(SQRT(2*(("Diameter"/2)*("Stick Reading"+"Striker plate"))-("Stick Reading"+"Striker plate")^2)*(("Diameter"/2)-("Stick Reading"+"Striker plate"))))/231]

Step 3: Tank Tilt

Fill point 1: 78.75 inch
Fill point 2: 75 inch
Distance between to two fill point: 198 inch
Difference is: 78.75(in)-75(in) = 3.75(in)
The ratio is: 256(in)/ 198(in) = 1.29(in)

So the tank tilt is: 1.29(in) * 3.75(in) = 4.85(in)

So I know the Tank Tilt, but what formula should I use to find out how much volume is in the tank when measuring from fill point 1 only. I'm sure it is more than the 7,062.54 Gallons from step 2.