Heya -
I'm Mike, the developer that wrote the spanned media support. Thanks so much for the kind words.
Writing spanned media support was one of my favorite features so far, due to the algorithmic constraints on the process, and the large number of conditions that the algorithm supports. SmartWIM relies on wimgapi for splitting sizes, and cannot generate a split part less than the size of the largest file. So, we use this size to determine our minimum split size, work backwards from the maximum split size allowed on the first disk until the number of discs generated matches what we have projected. This is simplifying the process a bit, but more or less how it works...
Mike