Are y'all talking about temp drop from strike water to end of mash? As opposed to stabilized temp with water and grist to end of mash? I admit that I lose 10 - 20 degrees from HLT to stabilized temp, but I lose only about 1 - 2 degrees even over 90 minutes in my Rubbermaid cooler once I've thoroughly doughed-in and closed her up. And I mash outside even when it's snowing and I routinely leave my cooler on the ground. And I don't preheat at all. I also monitor the temp continuously with an oven thermometer with the cord coming out from underneath the lid.
Just curious, because y'all seem to have a lot of heat loss.