Factors affecting sound attenuation

In cavity wall and floor construction the sound attenuation can be increased by

increasing the mass per unit area of the materials on each side of the wall or floor. The greater the weight per unit area, the better the sound insulation.
eliminating all solid connections between each face of the wall or floor
increasing the cavity depth
increasing the thickness of the sound-absorbing material in the cavity.
increasing the distance between studs or joists
increasing the distance between resilient metal channels

Some of the factors above are more important than others. Some may be insignificant in certain types of construction. The type of sound-absorbing material sometimes has an effect on the sound insulation and sometimes it does not. The algorithms take these factors into account and give predictions of sound ratings for common wall and floor constructions that satisfy the important requirements above.

If you cannot get an estimate for a particular construction, there are two possible reasons.

The design you are using does not give good sound insulation and so is not considered. For example, there are no resilient channels and gypsum board is attached directly to wood joists.
The design parameters exceed those used to develop the regression equations used in this program. The errors associated with predictions made for such designs would have unknown error limits.