There should be a way to give customers / end users an approximate wait that is not a function of available techs, but rather overall wait of existing customers in session.
Right now customers see availability / session waits based on representatives not assisting customers, which skews actual waits. Average wait time isn't good either because as more people queue up--especially in quick succession, that drives overall wait down. However, using the longest wait would give customers joining an indication of what they may be expected to see. That wait would adjust as that customer is helped out.
Position in Queue: # | Longest Wait 00:00:00 | Your Wait: 00:00:00