The development of the Continuous Feed Physical Vapour Transport (CF-PVT) process requires a perfect control of each phenomenon in the growth cell. Along this line, the present paper gives some inputs on the CF-PVT mass transfer regimes with respect to the process parameters, both from qualitative and quantitative viewpoints. For example, two boundary cases have been evidenced depending on the temperature. At low temperature, the growth is limited by the sublimation step between the source and the seed. In this case, the CF-PVT process can be roughly assimilated to the classical seeded sublimation technique. At high temperature, the process is limited by the feeding step, i.e. the CVD deposition and infiltration on the lower part of the source. Measurements are correlated to in-situ X-ray imaging. The ability of the X-ray imaging to in-situ qualify and quantify the mass transfer is discussed.