trunk extension cap plug

had AMD truck extension welded into the '68 Barracuda as part of the body rebuild.
The major body work is all done and I am installing the plastic cap plugs to cover the
holes in the sheet metal.

the L and R side trunk extensions each have an approximately 1 3/4 inch hole in them that should take a plastic cap plug. But the hole is not completely round, it has an obvious flat on one side.
I have attached a link to an AMD photo of the part and the flat is apparent. The flat is at about 11:00 on the hole.

Trunk Floor Extensions | AMD 840-1267-L

So did AMD mess this up, or is the flat as the hole was designed back in the day ? And if flat stays,, is there a special plastic plug for that hole?

thanks