One of the things I have wondered about is that several respected woodworkers have glued the side boards to the legs, a cross grain joint. Because the side boards are so wide, shrinkage is a major issue, particularly here in Oregon where we have hot dry summers and cool wet winters. According to the Woodweb calculator, and assuming the moisture content ranges from 7 to 14%, this could be as much as 5/32". Perhaps extreme, but it convinces me to take shrinkage into account.
I have decided to deal with shrinkage by floating the torsion box on the legs. I will glue and peg the bottom of the side boards to the legs and extend them 1/4" above the top of the legs. The 6" transverse bearers will rest on a 6" ledger glued to the side boards, which will allow the sideboards to expand and contract freely without affecting the top. This ledger also serves as a long stretcher and will keep the bench from racking. As a result, my bench will be like the Nicholson plate in not having a long stretcher across the bottom.