In considering this, keep in mind that there is apparently more one Cardassian controlled sector. In "The Wounded", the Enterprise traveled through parts of several sectors to find the Phoenix.
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"A gathering of Angels appeared above my head. They sang to me this song of hope, and this is what they said..." -Styx
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new siggy coming soon.
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"The Earl of Sandwich invented the sandwich. Samuel Morse invented the Morse Code. Plato invented the plate."
-Holly, Red Dwarf: "Parallel Universe"
One can see that sectors aren't named or numbered in any obviously systematic way, except for the crude division of 2-and 3-digit ones near Romulus, 4-digits near Klingons and 21000 numbers near Cardassians. There are probably more exceptions than there are known rule-following sectors - for various historical reasons we are not privy to. Later, when the Federation expands, the internal sector grid may slowly be simplified and systematized. Or then not.
I personally think that the internal, uncharted Cardassian space is divided into regular 20x20x20 ly sectors while the DMZ region has irregular, smaller sectors. In any case, the DMZ consists of multiple sectors, and many of those may have borders near Bajor to give our heroes quick access to them.
Timo Saloniemi
ensign: "Captain, picking up a Romulan fleet heading in our direction, five sectors away."
captain: "100 light-years? Fine, we have plenty of time to get away."
ensign: "No, sir. In this region, sectors are only half-a-light-year across. In fact, the Romulans are already here and are firing at us."
captain: "Damn you, Starfleet Department of Stellar Cartography!"
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"The Earl of Sandwich invented the sandwich. Samuel Morse invented the Morse Code. Plato invented the plate."
-Holly, Red Dwarf: "Parallel Universe"
And a 20X20X20ly cube isn't very practical when high-performance ships spend weeks crossing them. A Fed police corvette tailing a civilian ship suspected of aiding the Maquis: "Ship in sector 21345... Visits a planet in sector 21345... Moving on to a planet in sector 21345... Two possible Maquis ships reported in sector 21345 - might they be heading for our prey? Where was she again? Sector 21345?"
But as you say, Rick Sternbach apparently has an idea or two on the sector system. We should find out sooner or later...
Timo Saloniemi