You can do either depending on what you want to do. On a quilt with sashing you could do a feather the length of each block as separate feathers and it would look good. You can feather out from the corners to the center of each side. You can feather out from the center of each side to the corners. You could do sets of two feathers, one in each direction with a teardrop or circle where they join and use that motif several times along the border. The possibilities are endless.
Look around on YouTube for examples, Jamie Wallen has some good info, Angela Walters has a whole crafty class on feathers. You've already looked into Patsy Thompson who is awesome.
Most of all, enjoy. Feathers look great in borders no matter how you decide to do them. Can you tell feathers are my favorite?