When stacking bales, it is often thought that the interior toe ups should be placed the same distance from the exterior plane of the wall as the width of the bales, in other words, 18″. In truth, this is not a good idea. It is best to space the toe ups so that the interior plane of the toe is about 1″ bigger than the overall bale thickness. This allows for adjustments in the bales to achieve a flat wall in a minimum amount of time. It ultimately takes a bit more plaster to complete this system, but it is well worth the effort.
Another place to consider toe up placement and bale thickness is when stairs are framed in against a bale wall. For example, code calls for 36″ clear space for the stairs. If you place your toe ups any closer than 2″ from the edge of the stairs, you run the risk of not passing your final inspection. This is true because the 1 1/4″ plaster (roughly) would extend into the plane of the stairs. We hold our stairs to 39″ in rough frame rather than 36″. I suggest you do the same to avoid problems down the road. Even if you end up with a stairway that is 2″ bigger than code minimums, you will be happy you did it. There is nothing like having a finished house that the inspector will not pass on final inspection because of a tight stairway.