A statistical analysis has been made of 26 Polar Mesospheric Summer Echoes (PMSE) active modulation experiments between 2002 and 2007. Observed with the EISCAT VHF radar the PMSE signature can be reduced by means of heating the ionosphere with powerful high frequency (HF) radio waves. However, PMSE modulation experiments sometimes fail. We use a computational model to estimate the enhanced electron temperatures due to ionospheric heating from HF radio waves in the D-region. We show that the statistical PMSE modulation for a fixed HF heater-induced electron temperature enhancement appears to be independent of altitude. In addition, for experiments where the PMSE modulation experiment failed, we show that the atmospheric attenuation of the HF heater wave was too great for the HF wave to have any effect on the PMSE layer.