AFAIK These linetypes get their origin from where you start the slab, then just follow the polygon you draw.
You could get a few to line up nicely, by starting them both in the same location and modeling them in the same direction (using the polygonal geometry method), but you could easily find yourself chasing your tail when the problem occurs with the junctions of other slabs.
I don't know of any other way around it.
Cheers,
Link.