As I promise to derive more.... Below r the general convention for glass thickness calculation, as you can see the length taking account in term of constant ratio (β) versus height, therefore the impact would be negligible in normal condition unless exceed certain matrix.
But on the other hand, look at the Height (H) in the notation, it play dominant effect as one of the key variable.
Pls find the notation below:
Glass thickness = ( (β x (H^3) X 0.00001)/B )^0.5
β = A constant ratio between length over height
H = height of Tank
Bending Stress ( B ):Tensile Strength / Safety Factor
Just share my tot..... Hopes above helps.... Cheers..