Getting a chest for a teammates S grade shouldn't require a pre-made.

It simply shouldn't require them to be in your pre-made.

There are various reasons why people might not get to be in pre-mades often enough to acknowledge the feature.

In my case I work rotating shifts, so my friends old and new tend to be on very different schedules from myself.

It's getting rather annoying to see teammates I helped a lot get an S for what they did, and we're both playing a champion I own, but I don't get a chest because we queued separately.

Likewise when I get the S it sucks to know a teammate that helped me get it doesn't get a chest for their efforts.