Setting User Wall Heat Flux Coefficient Specification

Hi, I'm now doing with some simulation heat transfer through a channel, I'm stuck with the boundary condition. I have to set a specified heat flux (about 400 W/m2), I found on the documentation that I have to set value for 4 parameters A B C D, but I don't know what is the exact value for these values, I tried to set A = 400 and the others are 0, but it seems wrong. Can anyone experienced with this help me? Thanks a lot.

https://preview.redd.it/m6fgc6eutree1.png?width=756&format=png&auto=webp&s=fe27a6c2dd8af42a4ddaa0ceba7491e21b2e9d45