Shields addon: it is pretty clear torp shield are different from ship shields. The latter are transparent when raised, but not deflecting, and when they deflect, they only glow slightly and remain mostly transparent even then. Torp shields, by contrast, are opaque and glow even when let alone. So either torp shields operate on entirely different principles (and cannot be bigger), or, more likely, they are extremely overloaded compared to standard shields - which means they burn out quickliy.
Note: if you can build a generator that supports(given volume and shield surface) 1 PW/m^2 and hold days, OR build a generator that supports 1 EW/m^2 and holds minutes, doesn't mean you can build a generator doing both.
And I don't think power output of a generator is proportional to third power of its size. If, for example, the limiting factor is plasma flow, the output would be proportional to pipes cross-section and so to the second power of size. The ENERGY RESERVES go with the third power , but not output. A 10 times smaller generator would put 100 times less energy , though for 1/10th of time only.