Set Piece Requirements

[skittles sour]

So I'm trying to a do a mod that'll spawn the Herald Ruins entrance on a minuscule island in the middle of a lake filled with tentacles. And I tried spawning world with this:

AddTaskPreInit("wild_ancient_ruins", function(self)
--	self.background_room = "rainforest_lillypond"
	self.room_choices = {
      	rainforest_lillypond = math.random(3, 4)
     }
end)

The gen would take a long time, and when it is indeed finished the snaptooth setpiece would be on rainforest turf in the biome adjacent to the lilyponds. And when I look through the logs I see this repeated again and again:

[00:05:15]: scripts/map/storygen.lua(269,1) Warning! Couldn't find a spot in wild_ancient_ruins for PigRuinsEntrance5	

I was looking through the files for the static layouts, but I do not see anything specifying that the entrance setpiece needs to be on land. So how would I override this requirement and force the setpiece to spawn in the middle of the water?