The trapezoidal filter mathematically produces a signal whose amplitude is proportional to the input signal, with multiplicative factors depending on Trapezoidal Rise Time (k) and Delay Time (M).
You can set two parameters: the Trapezoidal Rescaling (SHF) (reg 0x1n80) and the Fine Gain (fg) (reg 0x1nc4).
For a desired Fine Gain (fg) set the register (64K * fg * 2^SHF)/(k * M) where SHF is the closest power of 2 to k*M (see Trapezoidal Rescaling) and 64K is the normalization over 16 bits.