Great topic! I've been having the same issue with my 10gal igloo. My workaround has been to preheat, but then treat it like it was room temp for calculations. In going to mess with the specific heat setting and see what I come up with!
Well I have my specific heat set to .98 and that is mimicking what happened in real life on my last brew day. I'm brewing a lambic over the weekend and I'm going to try to use the new profile and see how it turns out ill keep everyone posted. It seems even between the same equipment there can be some variation.