People routinely succeed in fusing 0100-30 and 0113-30 in stripe and checkerboard patterns. I think that there may be something else going on here.
Looking at your cycle (and depending on the placement of your thermocouple), your firings be missing the annealing range.
If we were firing 6mm of glass in our kilns here, this is more what the cycle would typically look like:
Time Temp Hold
140' 538°C 10'
20' 663°C 30'
25' 810°C 10'
Full 482°C 60'
120' 371°C 0
Full 21°C 0
I am confident that if you use this fusing cycle, the pieces will not break, unless the kiln is not capable of cooling uniformly.
For more on annealing in general, you might be interested in checking out this presentation: http://www.bullseyeglass.com/education/ ... glass.html