Interferogram elaboration

Cordial greetings to all. I find it very pleasant to read the problems and solutions that are raised in the forum. By reading and rereading what they express, I have learned enough to make an adequate interferogram.

I have used the A Braun tutorial and others from 2021
I have numerous questions for the successful development of DinSAR in a mountainous relief area with a tropocial moist forest forest cover. It is a dam site in the tropical humid forest where the civil works of the project are concentrated in an area of ​​0.25 km2. I am interested in knowing if the surfaces covered with concrete present systematic deformations, such as surface subsidence.

The first to ask are:

If Bn (Bperp) = 0 and Btemp (days)> 100-200 days, does the quality of the interferogram to be constructed improve?
Or is it preferable to use successive radar images with a Btemp of 12 days? and then obtain the average offset of several interferograms

When developing the interferogram is where I have my greatest challenge. I must select the area avoiding incorporating forest and leaving only dewn surfaces covered with concrete.
In this case my questions are:
When unwrapping the interferogram is there a minimum area threshold to use?
If in the area of ​​interest, there are pixels with a high coherence value but also with low coherence, how do I proceed to obtain a suitable unwrapped interferogram?

My problem is that when using “subset” zones larger than the area of ​​interest, the unwrapped interferogram is a systematic color ramp to express the displacements, which as well expressed in the forum is an error indicator

If you work with Sentinel-1 data, short temporal baselines should be preferred, especially in areas with vegetation cover.
As your area of interest is a dam site, probably surrounded by vegetation, traditional DInSAR approaches are likely to fail, because unwrapping of the phase needs large areas with high coherence and clear patterns of fringes. This is not the case for small areas or objects, and you end up with rather randomly unwrapped phase which has no significant information at a specific area (= the ramp you currently observe).
Please keep in mind that DInSAR is used to get deformations of large areas and unwrapping only works if these are visible in the interferogram.
A nice example is shown by ASF:

Source: How to Phase Unwrap an Interferogram – ASF

If you have small targets and high proportions of phase decorrelation, approaches based on persistent scatterers might be more promising. StaMPS - Detailed instructions - #2 by ABraun