I'm working on a little project to make the IP houseboats look a little less like floating boxes and more like...houseboats. To do this I've made some of the hulls shorter and some more narrow, and it all works fine, except I can't figure out how to alter the size of the lots on top of the hulls - no matter, I've gone with a simpler solution and decided to try and use an object that leaves a floor cutout to just hide the excess tiles. Works fine, except I now have floating floor edges.

I know it's possible to hide those too; the ladders from IP hide the floor edges of tiles that intersect them (I presume it hides rather than deletes floortiles like stairs do because, when you remove the ladder, the floortile is still there). I also created a basement under the forward part of the hull, added a row of ladders, and the floortile edges disappeared there, too, on tiles that are supposedly undeleteable. I've compared the object I'm using and the ladders to try and figure out the parameter that makes the floor edge hidden, but I can't quite figure it out. Any ideas on how to go about this?