crossref problem

On the attached image, I have a point on top of every roof surface. I wanted to draw a line from each tower (grey red objects) to every point, but I don't appear to be able to do it. I thought that plugging in the center points on the towers into A and all the roof points into B into CrossRef then into Ln would do it, but it appears to have a random result (though I'm sure its not!) - have I missed something? Any pointers would be great. Many thanks.