The current format certainly keeps events efficient, however assuming the worst is behind us with Covid do you want to continue turning members away? I come from a very large region where entries were anywhere from 150-200 pretty regularly, and we always finished by 4-5 PM while sill allowing 4-5 runs. In fact we used a similar format of AM-PM groups so that you didn't need to commit to a full day.
I'm not sure how many people are getting waitlisted in the current format, but it seems like not more than 20 or so...so even with 150 entrants I don't see why we couldn't offer the same 4-runs we get now. One of the negatives of the Covid-modified structure is not allowing afternoon entrants on site before noon, this potentially pushes back the afternoon start time. If you set up registration at a different location from the timing area, folks running in the afternoon could arrive by say 11:00 and be teched and registered so that they could do course walks immediately after the AM groups end and start back up sooner.
Just some thoughts, but I personally feel limiting entries to 100 and turning people away is not ideal.