U-center does not modify the individual satellite C/N0 values. Those values are reported in GSV, SAT, SVINFO messages.
The "avg" values are calculated; min/max are just stored. The usual computation of these values is based only those satellites used in the nav computation except for the cells in sky view.
The sky view pattern is best for assessing antenna sensitivity pattern if the UUT is mounted in open sky, no obscuration with PCB orientation(with respect to North and horizon) known and fixed for 24 hours.
Better indicators are in MON HW: AGC, noise, CW jamming and any changes when you enable/disable nearby electronics.
At best, chip antennas are are challenge due to inherent loss from linear polarization and omnidirectional pattern compared to upward view of patch.
The only not-easily-detectable RFI is pulsed jamming--- either CW or broadband...that needs a fast spectrum analyzer. Pulsed jamming may be so short that it doesn't affect C/N0 or AGC or other metrics, but it destroys the data bits in the 50 bps GPS datastream, forcing the receiver to await another 30 second cycle for the damaged data block to reappear.
Ground plane size and absence of ANY noisy currents through the ground plane are essential to chip antenna success.