Gravfft for combined load

Hi, everyone.
I have a question about the use of the «gravfft» module, according to the manual and some tests I made we can model the coherence or the admittance for a surface (Top) or sub-surface load (Bottom) by this module. Is it possible to model these two parameters for a combined load (Top and Bottom) at the same time and vary F, the ratio between the subsurface and surface load, and Te to find “the best fit parameters” with the minimum RMS.
Thank you.