I realize some stoves have some trick internal plumbing. I have used a temp gun on a few stoves to check water jacket temp, 40 degrees bottom to top difference was typical. Also I think it was an 80s Aqua II I disected put an internal domestic hot water coil internally and placed it mid point in the tank I guess since it didn't have to be as hot. Just my 2cents.
Randy
This is where things take down s different path. If there is water colder than 136 degrees making contact with the water jacket,that allows moisture found in the fuel we burn to gather in those spots, not all of it but some. 100 pounds of wood. 30% water, that's 30 pounds of water that has to go out the stack, if there are surfaces inside the firebox cooler than 136, some of that moisture gathers there, the moisture combined with ash and creates an acid that can eat things up fast. That'd why cb requires boiler protection systems, to make sure return temps are above 140 to keep cold spots from forming allowing condensation inside the firebox.
That's also why you see issues around the doors, the door doesn't have 180 degree water around it, it has air that may be -20, creating a cool spot for moisture to gather and bond with ash and cause problems
Hope that helps, stuff like that, is where some real problems exist