I think that this is right. The thing wouldn't rise at all. But the essence of steaming a pudding (and the pain in the ass of it) is controlling the heat by having a constant level of steam. For constant, don't worry about it heat; SV is the thing. Why not just plop your vessel into the SV so it is ~ 50% immersed and cover with the traditional towel. I'd pick a higher temp...90C? so as to get close to steam and keep your times the same. I'm very interested in your expt. This year we abandoned the steamed persimmon pud because of the PITA factor and made individual sticky toffee puddings (which were great BTW). Yes you are probably correct, but I was looking for the 12 hours time to make the meat really tender, which I don't think I would get with conventional timings ????