So it turns out that this is only configurable for TT events, but not group rides. Sorry!
In terms of configuring how late join works on a preference per user basis, that’s something that sounds tricky. I’ll flag with the team anyway and see if it’s something we can look at.
I thought that this will be tricky.
But I would like you to think about the idea to only have event with leaders drop the rider with the leader. Where there is no leader the rider should start from the pen.
Understood but this takes away one of the best part of group rides, the draft!
I get that a number of you would like to be able to ride the whole route, but I don’t think that this is a general consensus.
I had to try. 
This is probably the reason why I don’t do these big events, Training time is #1 priority.
And I’m not saying it’s a terrible idea, but I think if we made this mythical change that people should have the right to choose.
I agree changing this may break the internet. LOL
An example is yesterday.
I wanted to ride about 30 miles to get XP.
Got home late and decided to late join a ride for 30 min then start a full ride on a rebel route.
It was right at 25 min after the hour so I logged on selected a ride and ran up stairs to change clothes.
I had inadvertently signed up for the C ride and it put on route 0.6 mi from the end and by then, it was too late to switch to another ride (for double XP).
Not a deal breaker but options are nice.
To me the best part of a group ride is not the draft, it is the group.
Edit: and I would prefer the choice as to whether I earn the reward, unlock, badge etc.
Edit again: and if I want the best of both worlds I make the effort to be there on time. ( or warm up and join an hour later !)