The reason SBLink likes to zero from the spoilboard is because plywood varies in thickness. When doing joinery, this variance can have a big effect on joinery fit. When zeroing from the spoilboard, the tolerances you've set in the tools database and eCabs can be much better achieved. Plus if you are cutting plywood with eCabs, if you have a common place it can always go to to zzero, you don't have to be there with the zero plate to get it to zero out. But, I guess if you want to zero from the top of the material, I'd be interested how the joinery works with that method, as I've never zeroed that way.