so I’ve been going through the numbers, the setup all looks correct and on board so that leads me to this hypothesis:
a strong bronze steam engine gives an output of 24 - 96 KU/t on 96 - 384 steam/t, at 256 steam/t that’s something like 63.36 KU/t if you calculate as 256/96 steam/t (2.666 repeating ratio) or 64.08 KU/t 24 x 2.67 ratio.
Basically I think the fraction is messing things up and pushing the number off 64 KU/t exactly.
The strong steel boiler has a 32 - 128 KU/t output on 128 - 512 steam/t so at 256 steam/t that would output exactly 64 KU/t (256/128 = 2 ratio = 32 * 2 ratio = 64 KU/t) hence why it works perfectly.
I’m not a math man though so I think I need @Gregorius to confirm if my suspicions are correct here.
What do you think Greg?