Flare the feet and keep the legs relatively straight
The instructor uses rotated feet and relatively straight legs to match lower-body rotation in the single-plane setup. He says excessive knee flex inhibits rotation, while pushing the pelvis back and aligning the ankle with the back frees rotation and helps retain body tilt.
Channel: Todd Graves
Watch official source at 4:32Why this context matters
The setup is taught as part of a single-plane swing model.