question about measurement CBCPW circuit using CPW probe

Should the transition CPW to CBCPW (conductor-backed CPW) be needed when CPW probe is used to measure the CBCPW circuit? As you know, the mode of CBCPW is different from that of CPW, especially when the thickness of the substrate is very small. In this case, the impedance of CPW is different from that of CBCPW.

any answer?

In my view, You are right that we need to place the transition before measurement.
The next question is how can measure the CBCPW alone?
The anser is using de-embedding procedure.