I would rather have a gap, than not have a gap. With a gap the module is still usable, without a gap it is questionable. I have used the edge of the Kato railer and let that determine the amount of overhang from the side of the module, it about lines up with the back of the half tie. When you are making your own modules, this is something you can and must control. Do not just look at a spec and say 24 5/16", cut the top a little long, put the track on top, get your set back at one edge and then mark the other side and cut to length, unless you forget and cut inside the mark you should be OK. (How do I know, I have been there and done that, a large gap results).