Ion acoustic wave regime

I am fairly new to plasma physics and am making a project on the Ion Acoustic Wave. We have discussed Landau-damping in a plasma where we took the electrons to have a Maxwellian distribution and considered ions as immobile. The idea of the project is to generalise this to the case where we also take ions into account.

In my attempt to do so, I have used Python to solve the dispersion relation numerically. I find that for a temperature ratio $T_{el}/T_{ion}= 10^4$ and mass ratio $m_{el}/m_{ion}= 1/2$ the damping effect is weaker for the IAW than when the ions were considered immobile. How could I understand this result more intuitively? I was expecting the wave to damp faster as there are now two species absorbing energy from the wave. I also found that for heavier ions, the IAW gives almost identical results as the initial plasma model.