Edit: @phector2004 sounds right. I guess the collision box depends on where the origin of your object is.
I think you need to change the x value here. It looks like a normal fence has it’s origin at the endpost. The collision goes 0.25 voxels in one direction (that’s to cover the post), and 1.25 voxels in the other direction.
Try changing 1.25 to 0.5 and see what happens. I think that should chop it off but I haven’t really played with the collision boxes before so I could be wrong.
What you are trying to do requires you to place the collider in just the right spot. The game has some debug features which can visual a collider in the game. This should make it easy to get it in just the right spot.
It would be nice to have a tool which made making the collisions a lot easier. I tell you that.
Instead of making a new thread, I have come across a problem. When I build a house now, only the first layer of the roof is created and then building stops, leaving me with an open roof. Without the endpieces mod the roof is created.