[Greyjoy]

Last time I checked, clams were invisible to the graph, so the reality's probably even worse.

R'lyeh's just spamming the hell out of Voice of Tiamat. Between that and his bazillion astral mages, he can sitesearch all 20+ of the map's water provinces for five types of site pretty painlessly. Six if he designed his SC with a dash of nature or death. And it's not actually a BAD idea to convert a lot of those gems you won't be using anyway and drop Akashics on captured land provinces. (It may be a bad idea to do it on sea ones, though, unless you see weird scales and really want to reveal the site causing them. Or have ludicrous amounts of gems and forgot to bring a nature caster to find kelp forts.)

Strictly speaking, it's not IMPOSSIBLE to bring more players to bear, especially if someone's getting hit hard on the other flank; on the other hand, best-case scenario leaves you with a pretty lengthy and of necessity very thin supply line, for a gain that may or may not be worthwhile. Depends whether you feel that stopping, let's say, Ashdod is worth committing some of your armies to a risky task as opposed to eating the buffer state outright and praying you can handle the threat on the other side.

Don't underestimate the power of gem donations, though. A couple (dozen) good thugs can turn quite the tide.