What Id like to mention is that the S1A needs cor. accuracy 0.1 in azimuth and 0.8 in range to avoid the jumping phase, especially if the study area is located in two or more than two bursts, that also what I personally phased in my PhD using the ERS-1\2 and ENVISAT,
You could find more details about this in
22.214.171.124 image co-registration
in the following reference
"Although the processing of the IWS (TOPS) mode requires additional processing steps and the coregistration has to be performed with the precision of 0.001 pixel (in the azimuth direction), if an area within one burst is processed, such a precise coregistration is not necessary."
You could find more details in the following reference
(SENTINEL-1 INSAR PROCESSING OF CORNER REFLECTOR INFORMATION IN THE NORTHERN-BOHEMIAN COAL BASIN)