One way to facilitate being Centered at Impact and with the Left Shoulder properly located (in relation to the Ball) is to begin that way. Here's how Larry Nelson goes about it. Take a look at his 'set' in Photo 1A (as he relates to the athletic posture of the baseball infielder). Can the Head get more Centered (between the Feet) than this? Has he maintained that Centered Head in his actual Address (Photo 1)? If it can get any better, using Homer Kelley's words, "I'll buy the beer."
Also, though this thread is focused on the Pivot and its Center, note Larry's Power Package alignments. The Arms are in a natual, unforced condition, with the Right Elbow bent nicely. Also, notice his Hands. Both Wrists are Level, and this positions the Hands (Photo 2) in a relatively 'high' position. However, they are not Uncocked, which would put the Left Arm and Clubshaft In Line (from a down-the-line view), obviously something that Homer Kelley did not recommend (unless the player uses that technique to intentionally 'zero-out' the #3 Accumulator).