After looking into this issue for a bit, I’ve found out that there unfortunately isn’t a way to programmatically access the “attach top/base” function. The Speckle revit connector uses Revit’s API to be able to make changes the model with a user’s data instead of using the traditional user interface. Autodesk currently doesn’t provide API access to the “attach top/base” functionality, and therefore we are unable programtically make this change to a revit model. There is a pending request for autodesk to add API access to that functionality that you can track here, but although it has a good amount of upvotes, I wouldn’t count on it being added any time soon because the request was created in 2016.
The bit of good news is that I was able to reproduce the ceiling issue and have fixed it in the upcoming release, 2.11, which is not currently out but will be out sometime this week. Also, I am working on the pipes issue and I hope to have that in the 2.11 release as well.