Increase Thermal Mass Surface Area - Ribbed Soffit

[jacksym]

I wish to determine the effect of increasing the exposed thermal mass such as a ribbed concrete ceiling soffit.

I believe one method to model this is to create a partition wall with a hole leaving a downstand at the top. As I understand components are not taken into account in the dynamic model.

To create the ribs, if I select sub space to maintain 1 zone, is there anything else I need to do to ensure dynamic modelling of air flow and thermal properties across the openings is maintained?

Or I am open to an alternative methods/recommendations.

Thanks