I can't place big electric poles on water without landfill when both the mods "Elevated Rails" and "Water-Friendly Walls" are enabled. The issue only seems to arise when both mods are installed alongside this mod.

Looks like this is an issue with the wall mod, they overwrite the big electric pole collision mask completely instead of removing layers. You might be able to get around this by disabling the startup setting on the wall mod for allowing it to be placed on shallow water, which will prevent it from overwriting the collision mask this mod sets it to, but I would report this to that mod author, as there isn't anything I can do about it. Sorry!

Idk why I didn't think to check that myself, but it looks like disabling that setting fixes the issue, while still allowing poles and walls to be placed on shallow water. I'm still a bit curious why the issue doesn't occur at all unless Elevated Rails is installed alongside the two mods.