Is the system actually in "N" only configuration?
WiFi-N does not get along well in a mixed mode environment (where there are "N" and "B/G" systems).
Do you have neighbors running on channel 11, 10, and maybe 9 ("N" uses a wide bandwidth, and even "G" overlaps with adjacent channels). So neighboring access points could be causing interference (granted, I wouldn't expect interference to directly affect signal strength -- but maybe the "meter" is taking into account packet loss problems, not just signal strength seen; pure signal strength would be reporting on the strongest access point on the channel).
Oh, also note that 802.11n was finalized in 2009 -- "draft N" is 2007; it may not be fully compatible in "N" mode with modern devices.
Some things that MIGHT help:
You should be using 2.5 Ghz if possible. 5 GHz not sure how well it works. Mixed definitely doesn't work with Nook.
Nook doesn't play well with N. Use a, b, or g.
If I read the specification sheet for that router -- it only supports 2.4GHz...
And I've not seen any Nook recognize a 5GHz (a or n) access point (mine has different SSIDs for 2.4 and 5, plus a third SSID for 2.4 "guest" access)
it's strange that it works fine, in N @ 270mbs if it's less than 12" away from the router.. i've switched modes to G (up to 54mbs), completely opened the router, and it does the same exact thing.. i've unplugged the router and let it sit.. turned it back on, same thing.. changed channels, including auto, and it's the same thing..
i'm fairly convinced it's the Nook Tablet, not my router..
as i've said, all other devices used see the router at 80% though walls, etc..
really disappointing.. i'm going to take it to the local B&N tomorrow and see if i can either swap it out, or return it..