Creating polarimetric Index with Sentinel 1

I am trying to create indices/features with simple arithmetic operations with polarization bands of GRD products. Things like (VV/VH) or (VV+VH / VV-VH) etc.

The pixel values are beta0, sigma0 and gamma0 coefficients and are in dB ~ (-25, 0) range.
Is it correct to use these dB values to compute different indices? Or I should create these indices using original (linear) amplitude values (before calibration) and then transform them into dB?