Yeah, your maths seems a little wrong there.
The smallest Steel Tank holds 1,152,000 mB of liquid. [32,000 x 3 x 3 x 4]
An EnderTech tank of the same size holds 1,024,000 mB of liquid. [512,000 x 1 x 1 x 2] (~28,444 mB/block)
This seems small, but naturally, as the EnderTech tank gets bigger...