Influence of surface type in VTT mould model

[roelhendrickx]

Hello,
I am trying to find out how the postprocessor uses the parameter 'surface type' in the calculation of the mould growth index M according to Hannu- Viitanen and Ojanen et al.. In the original papers I find only the material type. Intuitively I understand how the surface characteristics have an important influence, but is it also possible to disclose how it is mathematically incorporated? I have the impression that it influences dM/dt quite a lot, but that M_max is not affected by it?
Kind regards,
Roel