When I downloaded the game, while I didn't get the exact value, I did see it to be noticeably less than 640 blocks. It would seem 1 block is not the equivalent of 1 megabit after all. I apologize for any confusion I've caused with my error.
In any case, I've really be enjoying the game, but one nagging issue I still have with it is how small the 'aim-but-don't-move' section is on the Circle Pad. Between the dead zone and the movement zone, there's hardly anything to the aiming-only zone. It's extremely difficult to move the Circle Pad into it, let alone to stay within it, to where it often takes multiple attempts of accidentally walking/dropping through platforms into enemies/jumping off of rope into enemies before I can find it and start aiming. Consequently, this also means the caution required to stay in this section of the Circle Pad also makes aiming really slow. There exists X button lock on, yes, but I've found it fairly useless against targets that aren't moving straight towards you directly (slimes, demon eyes, worms, et cetera). I understand the desire to keep the dead and movement zones large, to compensate for 3DS systems with imperfect Circle Pad calibration or centering, but I would hope to see the aiming-only zone expanded in a future update.