I have a mod that has a solid named Super heat conductor and its heat conduct property is at 255 however it still conducts slower than Rapid heat conductor which only has 251 heat conductivity
HEAC uses a special code to transfer heat over a greater distance than normal to simulate significantly greater thermal conductivity (similar to how GOLD, PTNM and SLCN implement increased SPRK speed). To reproduce this behavior, you need to reproduce this code.