I'd have to rewatch the movie to be sure, but I thought I saw in TSFS an Enterprise bridge graphic that showed partial shielding at the point where Chekov said the shields were not responding, which if correct would suggest that it was a full-yield torpedo hit that struck partially-raised shields that let some damage through, sufficient to cripple Enterprise.
Of interest is that Enterprise's port torpedo tube had been destroyed in TWOK by Khan's megaphasers during the Mutara Nebula battle, so apparently Constitution-refits can fire two torpedos from each tube a half-second apart. Hitherto now, I thought it was only one torpedo at a time per tube, with a lengthy reload time (as shown in TWOK as Enterprise prepares for the final battle).
Regarding the megaphasers of Reliant, I tend to think that while the Constitution-refits and newbuild Constitutions are more exploratory ships than frontline combat vessels, while the Mirandas (Reliant's purpose of working with Project Genesis not withstanding) are designed more for frontline combat. This also helps to explain why Mirandas are seen in the TNG/DS9 era, especially during the Dominion War, though whether they're present as continuously long-serving starships or recently recommissioned from storage and supply depots for the DW is questioned.
Of interest is that Enterprise's port torpedo tube had been destroyed in TWOK by Khan's megaphasers during the Mutara Nebula battle, so apparently Constitution-refits can fire two torpedos from each tube a half-second apart. Hitherto now, I thought it was only one torpedo at a time per tube, with a lengthy reload time (as shown in TWOK as Enterprise prepares for the final battle).
Regarding the megaphasers of Reliant, I tend to think that while the Constitution-refits and newbuild Constitutions are more exploratory ships than frontline combat vessels, while the Mirandas (Reliant's purpose of working with Project Genesis not withstanding) are designed more for frontline combat. This also helps to explain why Mirandas are seen in the TNG/DS9 era, especially during the Dominion War, though whether they're present as continuously long-serving starships or recently recommissioned from storage and supply depots for the DW is questioned.