Each of the yards have unique constraints. Hopefully, the 2 to 4 increase is to be some sort of test such that the ability to stack 6/9 high is still within reason given it as the limit of the higher end stackers. Additionally, these https://www.youtube.com/watch?v=TSn-dT4EMcM do not require welding to transform; are quoted with the same strength, a quarter of the original size, and 20% more expensive in early 2017.