It sounds like you missed some of the generators on the northern group of islands.
Here is a
map, or from the
walkthrough;
-The anti-dragon zone on the southern islands can be disabled by destroying
the 17 generators on the northern islands.
-There are five generators on the very highest ring of outer islands (one on
each island except the northern one).
-Six generators sit on the large outer islands (one on each).
-The middle island has three generators near its center.
-The last three generators are hidden on small islands that lurk beneath the
larger outer islands (one to the north, one to the southwest, and one to the
southeast).
