SNe 2011dh and 1993J have been observed thoroughly in radio wavelengths over the past years. The very late time radio light curves of these two supernovae (SNe) have revealed a sudden downturn in the radio emission around 4000 and 400 days after the explosion of SNe 1993J and 2011dh, respectively. For SN 1993J, from the resolved VLBI image of SN shocks, it has been found that beyond around 4000 days the reverse shock is decelerating faster than the forward shock. Therefore, it is possible that the drop in radio luminosity is due to the fact that around 4000 and 400 days after the explosion the reverse shocks of both the SNe have started to enter into the innermost flat ejecta structure of the SNe. To investigate this possibility, we have carried out hydrodynamical simulations to evaluate the interaction of the SN ejecta and circumstellar medium (CSM), considering the ejecta structures of both SNe from numerical simulations. From spherically symmetric hydro simulations we found that for both the SNe the reverse shocks do not experience any drastic change in the density profile of the unshocked ejecta gas beyond 4000 and 400 days, and the radio fluxes, estimated from our radio modeling, at those epochs are more than twice as high as the detected flux post 4000 and 400 days. However, the radio emission up to around 4000 days is reasonably well predicted by our model for both SNe, assuming the mass loss rates of 0.9e-5  Msun/yr and 3e-7 Msun/yr for SNe 1993J and 2011dh, respectively (for v_wind = 10 km/s). It is therefore unlikely that the sudden decrease in radio luminosity is because of the fact that the reverse shock is experiencing a change in SN ejecta structure. A possible explanation of this drop could be a rapid decrease in the CSM density after a certain radius. We are currently exploring this possibility.