How do f-mode Frequencies Change with Solar Radius?

We test the relation between relative f-mode frequency variation and Lagrangian perturbation in the solar radius obtained by Dziembowski and Goode (2004) using several pairs of solar models and show that it doesn't hold true for any of the model pairs we have used. We attempt to derive a better approximation for the kernel linking the relative frequency changes and the solar radius variation in the subsurface layers