I only put in enough for my needs (double shot).
That way they are always as fresh as possible.
I have one of those trap doors (whatever its called) on my hopper that lets you remove the hopper with the beans still in it.
I can measure by eye how many beans I need when its shut and then open it to let the beans fall into the grinder; I then shut it again to act as a lid over the beans so they dont have as much room to bounce around.
With it open some beans do pop back up into the hopper as the grinding is taking place, so I know it helps to a small degree.
I dont prepare multiple drinks very often but when I do I dont notice any difference when I have more beans in the hopper to when I dont.
If you dont have the hopper door, I know some people place a lid or tamper over the beans as a cover or weight. *