1969 Camaro Carpet to Rear Interior Side Panel Fitment

[Krateness]

Hey everyone, I’m a bit lost on how these 2 pieces interact. I have the original carpet but was not the one who removed it to see how it was. I have the original interior side panel as well.

I’ve had a bunch of people tell me that it needs to be tucked and I’ve seen people say that the factory didn’t tuck it which a factory appearance is what I’m trying to do. If it has to be tucked what happens with the flap I’ve circled in red? Can’t be trimmed because my factory panel still has it complete. So it’s it tucked under and sort of pinched in this material?

Likewise if it isn’t tucked, how is it held/kept laid down against the panel?

Any help is appreciated