Radius Markers - Not working for sea creatures

[zombiezrule]

I'm trying to add radius markers for sea creatures (specifically the vampyre kraken), and using the ID from NPC ID (15212) doesn't give any radius markers around said NPCs.
Tried it for other NPC IDs nearby and they also aren't working.

[Skretzo]

I believe the problem is that your player character and boat is technically elsewhere than the sea creatures (in an instance). I would need to figure out how to translate the coordinates. I think you are able to see the radius marker on the sea creatures if you stand on land instead of on a boat, right?

[zombiezrule]

I don't know how it all works but it seems the Sailing plugin has got some markers working for shipwrecks, and tile indicators has tiles properly displaying on the sea area. So it seems like it's possible, unless Radius Markers works differently to those plugins.