We present the results of experimental investigation of a laboratory prototype of the electron-wave microwave amplifier for the case of great values of the inhomogeneity parameters of electron beam velocities. The influence of several factors on the gain of such systems in the case under consideration is demonstrated experimentally. It is found that at great values of the inhomogeneity parameters a significant increase in the power of the input signals leads to an increase in the gain of the system. The proposed scheme of operation of the electron-wave amplifier allows improving its stability, increasing the gain to about 20 dB, and reducing its size. The significance of the obtained experimental results and studied phenomena for advancement of the operating frequencies of electron-wave amplifiers into a shorter-wavelength band is shown.