Increasing value of displacement with increase height

[ABraun]

yes, after unwrapping it would be best. I’d say 0.3 or 0.4.
You can also make those areas zero

Coherence Mask/Threshold for Unwrapping

I would use the ‘valid pixel expression’ definiton in the band properties. For example: coh_HH_11Feb2008_04Mar2008 > 0.4 If you want to calculate a new raster you can also do it in the band maths: if coh_HH_11Feb2008_04Mar2008 < 0.4 then 0 else Phase_xx

To include the coherence layer in the final product you need to select it in the Range Doppler Terrain Correction module.