How to mange GNSS velocity of reference area in mean velocity and adjust cumulative displacement

I’m doing PS InSAR processing using SNAP and Stamps

  1. I managed to get the csv file from matlab. I follow below steps to set my reference area
setparm('ref_centre_lonlat' , [lon lat])
setparm('ref_radius', radius_m)

but my reference point also have GNSS station and it’s upward displacement is -110 mm/yr.

So i added this offset in third column of csv velocity. So if previous velocity was 15.367 mm/yr. The new velocity become -84.63 mm/yr. But to show time series i used the the values of cumulative displacemnet from third column to last column but it shows increasing trend as it is obvious that initially it was 15.367 mm/yr before adding offset value from GNSS station. So how to accomodate the displacement values also so that when i used scatter plot it show decreasing trend and slope equal to around -84.63 mm/yr.

  1. For PSI processing, I used images from ascending ( 2023 - 2034 ) time period and velocity range from -70.2 - 89.9 with 78 files and one is from descending orbit ( 2018 - 2024 ) and velocity ranges from -9.9 - 24.5 from 180 files , what is reason for such large difference. which one would be reliable to use?