Good point, that might very well be.
Though, since you can pay the heatup cost many times, while you have to pay the material costs for the fuel boxes and boiler blocks only once, I would still remain of a different opinion. It works in the special case of assembling the boiler once in a specific location and then letting it run until the twilight of the world itself, but that's just one case of many. As such you can't really use that model to make an universally applicable statement.
P.S.: I am the 5%