How wide do you want the knife pleat flange to be? I would suggest trying with some scrap fabric to just do the corner and see what you like. I'm thinking that one would need to gather what will be the inside edge of the corner if you want the flange to lay flat. Are you wanting it to look similar to the one seen at
https://www.newtoncustominteriors.co...-pleat-ruffle/ ?
Janey - Neat people never make the exciting discoveries I do.
Not affiliated with off-site link(s)