Up close as what we see on a regular basis in Trek. Stealth tech (cloaks, again, aside) isn't going to get you up close like we've seen regularly in post TWOK Trek. u
Actually that's pretty much the case for modern stealth fighters as well: if you're within dogfight range of an enemy aircraft, you're going to be visible to him no matter what you're flying; if he can't physically see
you, his radar definitely will.
Same in the more analogous case of submarines: once you get into (or close to) torpedo range you won't have THAT much trouble tracking your target; it's getting into range in the first place -- or knowing that there's anything there to get into range WITH -- that presents the real challenge.
My interpretation if cloaking devices is that they're a brute force method of achieving stealth: the enemy's scanning space, so you jam his sensors in such a way that he can't easily detect your ship unless he gets close enough to detect either your energy displacement or the radiation from your weapon systems. Vengeance's design may be a more passive approach: the enemy's scanning space, so you construct your starship out of a material and with a design that won't fully register on his sensors unless you're looking directly at it and you don't usually know where to look unless it draws attention to itself first.
FYI, there's already precedent for this in Trek: Baran's pirate vessel in "Gambit" is outfitted with EXACTLY this kind of technology, to the point that the Enterprise has difficulty tracking it at a distance and also has trouble scanning the entire of the vessel. The "stealth coating" on the pirate ship is primitive by 24th century standards -- if still marginally effective -- but in the 23rd, it's almost certainly cutting-edge.